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 $226.74   13.804%   $258.0392   $258.04   $258.05   $258.00  
  Purchase #2 $188.64   4.725%   $197.5532   $197.55   $197.55   $197.60  
  Purchase #3 $93.93   8.397%   $101.8173   $101.82   $101.80   $101.80  
  Purchase #4 $57.59   12.871%   $65.0024   $65.00   $65.00   $65.00  
  Purchase #5 $24.75   7.402%   $26.582   $26.58   $26.60   $26.60  
  Purchase #6 $231.93   9.588%   $254.1674   $254.17   $254.15   $254.20  
  Purchase #7 $37.53   9.499%   $41.095   $41.10   $41.10   $41.10  
  7 purchase totals = $861.11       $944.2565   $944.26   $944.25   $944.30