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 $56.57   8.691%   $61.4865   $61.49   $61.50   $61.50  
  Purchase #2 $130.26   5.173%   $136.9983   $137.00   $137.00   $137.00  
  Purchase #3 $56.35   6.275%   $59.886   $59.89   $59.90   $59.90  
  Purchase #4 $229.62   7.298%   $246.3777   $246.38   $246.40   $246.40  
  Purchase #5 $234.29   11.834%   $262.0159   $262.02   $262.00   $262.00  
  Purchase #6 $93.25   8.571%   $101.2425   $101.24   $101.25   $101.20  
  Purchase #7 $51.93   3.476%   $53.7351   $53.74   $53.75   $53.70  
  7 purchase totals = $852.27       $921.7420   $921.76   $921.80   $921.70