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 $54.37   11.335%   $60.5328   $60.53   $60.55   $60.50  
  Purchase #2 $92.38   13.395%   $104.7543   $104.75   $104.75   $104.80  
  Purchase #3 $104.57   10.600%   $115.6544   $115.65   $115.65   $115.70  
  Purchase #4 $135.87   9.755%   $149.1241   $149.12   $149.10   $149.10  
  Purchase #5 $69.35   6.825%   $74.0831   $74.08   $74.10   $74.10  
  Purchase #6 $195.25   4.326%   $203.6965   $203.70   $203.70   $203.70  
  Purchase #7 $238.33   7.296%   $255.7186   $255.72   $255.70   $255.70  
  7 purchase totals = $890.12       $963.5638   $963.55   $963.55   $963.60