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 $202.31   12.164%   $226.919   $226.92   $226.90   $226.90  
  Purchase #2 $195.52   10.804%   $216.644   $216.64   $216.65   $216.60  
  Purchase #3 $51.72   12.613%   $58.2434   $58.24   $58.25   $58.20  
  Purchase #4 $205.67   12.865%   $232.1294   $232.13   $232.15   $232.10  
  Purchase #5 $72.77   4.312%   $75.9078   $75.91   $75.90   $75.90  
  Purchase #6 $150.41   5.425%   $158.5697   $158.57   $158.55   $158.60  
  Purchase #7 $107.41   4.527%   $112.2725   $112.27   $112.25   $112.30  
  7 purchase totals = $985.81       $1,080.6858   $1,080.68   $1,080.65   $1,080.60