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 $238.63   11.802%   $266.7931   $266.79   $266.80   $266.80  
  Purchase #2 $68.64   11.179%   $76.3133   $76.31   $76.30   $76.30  
  Purchase #3 $21.61   13.135%   $24.4485   $24.45   $24.45   $24.40  
  Purchase #4 $202.97   11.733%   $226.7845   $226.78   $226.80   $226.80  
  Purchase #5 $91.53   4.585%   $95.7267   $95.73   $95.75   $95.70  
  Purchase #6 $232.26   4.375%   $242.4214   $242.42   $242.40   $242.40  
  Purchase #7 $15.34   5.363%   $16.1627   $16.16   $16.15   $16.20  
  7 purchase totals = $870.98       $948.6502   $948.64   $948.65   $948.60