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 $213.82   8.374%   $231.7253   $231.73   $231.75   $231.70  
  Purchase #2 $136.62   8.227%   $147.8597   $147.86   $147.85   $147.90  
  Purchase #3 $173.92   12.137%   $195.0287   $195.03   $195.05   $195.00  
  Purchase #4 $56.35   5.387%   $59.3856   $59.39   $59.40   $59.40  
  Purchase #5 $108.35   10.349%   $119.5631   $119.56   $119.55   $119.60  
  Purchase #6 $55.54   8.409%   $60.2104   $60.21   $60.20   $60.20  
  Purchase #7 $67.65   5.455%   $71.3403   $71.34   $71.35   $71.30  
  7 purchase totals = $812.25       $885.1131   $885.12   $885.15   $885.10