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 $105.81   7.506%   $113.7521   $113.75   $113.75   $113.80  
  Purchase #2 $57.35   5.271%   $60.3729   $60.37   $60.35   $60.40  
  Purchase #3 $51.57   7.722%   $55.5522   $55.55   $55.55   $55.60  
  Purchase #4 $244.91   8.326%   $265.3012   $265.30   $265.30   $265.30  
  Purchase #5 $33.96   5.346%   $35.7755   $35.78   $35.80   $35.80  
  Purchase #6 $125.76   12.753%   $141.7982   $141.80   $141.80   $141.80  
  Purchase #7 $222.28   7.302%   $238.5109   $238.51   $238.50   $238.50  
  7 purchase totals = $841.64       $911.0630   $911.06   $911.05   $911.20