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 $75.44   11.364%   $84.013   $84.01   $84.00   $84.00  
  Purchase #2 $71.44   3.264%   $73.7718   $73.77   $73.75   $73.80  
  Purchase #3 $131.80   9.220%   $143.952   $143.95   $143.95   $144.00  
  Purchase #4 $56.82   11.266%   $63.2213   $63.22   $63.20   $63.20  
  Purchase #5 $200.90   11.871%   $224.7488   $224.75   $224.75   $224.70  
  Purchase #6 $212.61   10.617%   $235.1828   $235.18   $235.20   $235.20  
  Purchase #7 $46.93   13.139%   $53.0961   $53.10   $53.10   $53.10  
  7 purchase totals = $795.94       $877.9858   $877.98   $877.95   $878.00