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 $119.85   13.841%   $136.4384   $136.44   $136.45   $136.40  
  Purchase #2 $166.25   6.379%   $176.8551   $176.86   $176.85   $176.90  
  Purchase #3 $230.33   4.538%   $240.7824   $240.78   $240.80   $240.80  
  Purchase #4 $181.47   13.463%   $205.9013   $205.90   $205.90   $205.90  
  Purchase #5 $191.63   13.864%   $218.1976   $218.20   $218.20   $218.20  
  Purchase #6 $212.38   6.397%   $225.9659   $225.97   $225.95   $226.00  
  Purchase #7 $74.54   5.552%   $78.6785   $78.68   $78.70   $78.70  
  7 purchase totals = $1,176.45       $1,282.8192   $1,282.83   $1,282.85   $1,282.90