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 $245.55   11.107%   $272.8232   $272.82   $272.80   $272.80  
  Purchase #2 $55.60   4.218%   $57.9452   $57.95   $57.95   $57.90  
  Purchase #3 $224.57   7.446%   $241.2915   $241.29   $241.30   $241.30  
  Purchase #4 $20.62   9.782%   $22.637   $22.64   $22.65   $22.60  
  Purchase #5 $219.45   7.733%   $236.4201   $236.42   $236.40   $236.40  
  Purchase #6 $129.55   10.300%   $142.8937   $142.89   $142.90   $142.90  
  Purchase #7 $58.32   4.340%   $60.8511   $60.85   $60.85   $60.90  
  7 purchase totals = $953.66       $1,034.8618   $1,034.86   $1,034.85   $1,034.80