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 $191.70   10.414%   $211.6636   $211.66   $211.65   $211.70  
  Purchase #2 $34.54   9.119%   $37.6897   $37.69   $37.70   $37.70  
  Purchase #3 $58.62   7.219%   $62.8518   $62.85   $62.85   $62.90  
  Purchase #4 $247.28   11.733%   $276.2934   $276.29   $276.30   $276.30  
  Purchase #5 $208.73   12.614%   $235.0592   $235.06   $235.05   $235.10  
  Purchase #6 $54.60   11.300%   $60.7698   $60.77   $60.75   $60.80  
  Purchase #7 $98.60   12.519%   $110.9437   $110.94   $110.95   $110.90  
  7 purchase totals = $894.07       $995.2712   $995.26   $995.25   $995.40