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 $214.65   11.261%   $238.8217   $238.82   $238.80   $238.80  
  Purchase #2 $212.62   3.719%   $220.5273   $220.53   $220.55   $220.50  
  Purchase #3 $247.52   3.478%   $256.1287   $256.13   $256.15   $256.10  
  Purchase #4 $72.58   5.485%   $76.561   $76.56   $76.55   $76.60  
  Purchase #5 $220.74   3.864%   $229.2694   $229.27   $229.25   $229.30  
  Purchase #6 $197.56   13.487%   $224.2049   $224.20   $224.20   $224.20  
  Purchase #7 $55.63   6.363%   $59.1697   $59.17   $59.15   $59.20  
  7 purchase totals = $1,221.30       $1,304.6827   $1,304.68   $1,304.65   $1,304.70