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 $241.98   4.874%   $253.7741   $253.77   $253.75   $253.80  
  Purchase #2 $215.52   9.266%   $235.4901   $235.49   $235.50   $235.50  
  Purchase #3 $80.68   6.649%   $86.0444   $86.04   $86.05   $86.00  
  Purchase #4 $94.36   12.767%   $106.4069   $106.41   $106.40   $106.40  
  Purchase #5 $224.84   7.481%   $241.6603   $241.66   $241.65   $241.70  
  Purchase #6 $205.68   3.756%   $213.4053   $213.41   $213.40   $213.40  
  Purchase #7 $141.48   11.262%   $157.4135   $157.41   $157.40   $157.40  
  7 purchase totals = $1,204.54       $1,294.1946   $1,294.19   $1,294.15   $1,294.20