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 $180.47   12.227%   $202.5361   $202.54   $202.55   $202.50  
  Purchase #2 $61.53   4.667%   $64.4016   $64.40   $64.40   $64.40  
  Purchase #3 $31.38   3.695%   $32.5395   $32.54   $32.55   $32.50  
  Purchase #4 $210.27   10.187%   $231.6902   $231.69   $231.70   $231.70  
  Purchase #5 $192.38   8.220%   $208.1936   $208.19   $208.20   $208.20  
  Purchase #6 $131.64   13.508%   $149.4219   $149.42   $149.40   $149.40  
  Purchase #7 $188.52   9.534%   $206.4935   $206.49   $206.50   $206.50  
  7 purchase totals = $996.19       $1,095.2764   $1,095.27   $1,095.30   $1,095.20