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 $47.27   9.285%   $51.659   $51.66   $51.65   $51.70  
  Purchase #2 $228.89   11.661%   $255.5809   $255.58   $255.60   $255.60  
  Purchase #3 $198.54   9.795%   $217.987   $217.99   $218.00   $218.00  
  Purchase #4 $88.64   11.635%   $98.9533   $98.95   $98.95   $99.00  
  Purchase #5 $244.95   11.397%   $272.867   $272.87   $272.85   $272.90  
  Purchase #6 $68.68   9.679%   $75.3275   $75.33   $75.35   $75.30  
  Purchase #7 $58.46   12.360%   $65.6857   $65.69   $65.70   $65.70  
  7 purchase totals = $935.43       $1,038.0604   $1,038.07   $1,038.10   $1,038.20