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 $103.32   13.497%   $117.2651   $117.27   $117.25   $117.30  
  Purchase #2 $14.85   12.147%   $16.6538   $16.65   $16.65   $16.70  
  Purchase #3 $164.73   6.218%   $174.9729   $174.97   $174.95   $175.00  
  Purchase #4 $207.61   13.733%   $236.1211   $236.12   $236.10   $236.10  
  Purchase #5 $164.73   7.650%   $177.3318   $177.33   $177.35   $177.30  
  Purchase #6 $200.29   13.735%   $227.7998   $227.80   $227.80   $227.80  
  Purchase #7 $99.92   3.595%   $103.5121   $103.51   $103.50   $103.50  
  7 purchase totals = $955.45       $1,053.6566   $1,053.65   $1,053.60   $1,053.70