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 $243.75   6.858%   $260.4664   $260.47   $260.45   $260.50  
  Purchase #2 $43.53   6.310%   $46.2767   $46.28   $46.30   $46.30  
  Purchase #3 $88.27   3.641%   $91.4839   $91.48   $91.50   $91.50  
  Purchase #4 $30.62   9.578%   $33.5528   $33.55   $33.55   $33.60  
  Purchase #5 $90.81   9.251%   $99.2108   $99.21   $99.20   $99.20  
  Purchase #6 $221.78   13.733%   $252.237   $252.24   $252.25   $252.20  
  Purchase #7 $83.95   9.263%   $91.7263   $91.73   $91.75   $91.70  
  7 purchase totals = $802.71       $874.9539   $874.96   $875.00   $875.00