Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $231.60   13.118%   $261.9813   $261.98   $262.00   $262.00  
  Purchase #2 $147.44   6.258%   $156.6668   $156.67   $156.65   $156.70  
  Purchase #3 $197.92   3.669%   $205.1817   $205.18   $205.20   $205.20  
  Purchase #4 $154.61   10.809%   $171.3218   $171.32   $171.30   $171.30  
  Purchase #5 $208.77   10.494%   $230.6783   $230.68   $230.70   $230.70  
  Purchase #6 $163.26   3.532%   $169.0263   $169.03   $169.05   $169.00  
  Purchase #7 $106.44   10.659%   $117.7854   $117.79   $117.80   $117.80  
  7 purchase totals = $1,210.04       $1,312.6416   $1,312.65   $1,312.70   $1,312.70