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 $91.48   4.455%   $95.5554   $95.56   $95.55   $95.60  
  Purchase #2 $32.74   11.334%   $36.4508   $36.45   $36.45   $36.50  
  Purchase #3 $209.99   8.575%   $227.9966   $228.00   $228.00   $228.00  
  Purchase #4 $219.85   11.604%   $245.3614   $245.36   $245.35   $245.40  
  Purchase #5 $59.62   7.815%   $64.2793   $64.28   $64.30   $64.30  
  Purchase #6 $33.36   13.358%   $37.8162   $37.82   $37.80   $37.80  
  Purchase #7 $17.56   7.288%   $18.8398   $18.84   $18.85   $18.80  
  7 purchase totals = $664.60       $726.2995   $726.31   $726.30   $726.40