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 $108.72   10.833%   $120.4976   $120.50   $120.50   $120.50  
  Purchase #2 $42.36   3.429%   $43.8125   $43.81   $43.80   $43.80  
  Purchase #3 $146.46   13.801%   $166.6729   $166.67   $166.65   $166.70  
  Purchase #4 $29.51   7.264%   $31.6536   $31.65   $31.65   $31.70  
  Purchase #5 $209.69   13.200%   $237.3691   $237.37   $237.35   $237.40  
  Purchase #6 $136.47   12.613%   $153.683   $153.68   $153.70   $153.70  
  Purchase #7 $58.93   7.314%   $63.2401   $63.24   $63.25   $63.20  
  7 purchase totals = $732.14       $816.9288   $816.92   $816.90   $817.00