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 $68.93   8.866%   $75.0413   $75.04   $75.05   $75.00  
  Purchase #2 $120.76   12.557%   $135.9238   $135.92   $135.90   $135.90  
  Purchase #3 $222.41   4.714%   $232.8944   $232.89   $232.90   $232.90  
  Purchase #4 $194.78   9.215%   $212.729   $212.73   $212.75   $212.70  
  Purchase #5 $166.39   12.155%   $186.6147   $186.61   $186.60   $186.60  
  Purchase #6 $24.77   12.229%   $27.7991   $27.80   $27.80   $27.80  
  Purchase #7 $8.92   13.584%   $10.1317   $10.13   $10.15   $10.10  
  7 purchase totals = $806.96       $881.1340   $881.12   $881.15   $881.00