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 $59.34   8.741%   $64.5269   $64.53   $64.55   $64.50  
  Purchase #2 $236.59   10.840%   $262.2364   $262.24   $262.25   $262.20  
  Purchase #3 $205.65   13.823%   $234.077   $234.08   $234.10   $234.10  
  Purchase #4 $152.84   3.463%   $158.1328   $158.13   $158.15   $158.10  
  Purchase #5 $65.57   3.761%   $68.0361   $68.04   $68.05   $68.00  
  Purchase #6 $171.83   6.233%   $182.5402   $182.54   $182.55   $182.50  
  Purchase #7 $235.97   8.579%   $256.2139   $256.21   $256.20   $256.20  
  7 purchase totals = $1,127.79       $1,225.7633   $1,225.77   $1,225.85   $1,225.60