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 $194.65   8.277%   $210.7612   $210.76   $210.75   $210.80  
  Purchase #2 $11.51   5.271%   $12.1167   $12.12   $12.10   $12.10  
  Purchase #3 $39.50   7.186%   $42.3385   $42.34   $42.35   $42.30  
  Purchase #4 $56.28   8.771%   $61.2163   $61.22   $61.20   $61.20  
  Purchase #5 $206.75   5.809%   $218.7601   $218.76   $218.75   $218.80  
  Purchase #6 $56.93   13.382%   $64.5484   $64.55   $64.55   $64.50  
  Purchase #7 $184.90   3.103%   $190.6374   $190.64   $190.65   $190.60  
  7 purchase totals = $750.52       $800.3786   $800.39   $800.35   $800.30