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 $72.31   5.361%   $76.1865   $76.19   $76.20   $76.20  
  Purchase #2 $173.42   4.336%   $180.9395   $180.94   $180.95   $180.90  
  Purchase #3 $140.81   12.139%   $157.9029   $157.90   $157.90   $157.90  
  Purchase #4 $46.97   4.630%   $49.1447   $49.14   $49.15   $49.10  
  Purchase #5 $228.31   4.441%   $238.4492   $238.45   $238.45   $238.40  
  Purchase #6 $215.95   7.743%   $232.671   $232.67   $232.65   $232.70  
  Purchase #7 $111.84   5.195%   $117.6501   $117.65   $117.65   $117.70  
  7 purchase totals = $989.61       $1,052.9439   $1,052.94   $1,052.95   $1,052.90