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 $59.95   10.390%   $66.1788   $66.18   $66.20   $66.20  
  Purchase #2 $240.82   9.852%   $264.5456   $264.55   $264.55   $264.50  
  Purchase #3 $244.68   7.311%   $262.5686   $262.57   $262.55   $262.60  
  Purchase #4 $48.74   5.436%   $51.3895   $51.39   $51.40   $51.40  
  Purchase #5 $61.34   6.541%   $65.3522   $65.35   $65.35   $65.40  
  Purchase #6 $217.34   6.776%   $232.067   $232.07   $232.05   $232.10  
  Purchase #7 $107.36   10.701%   $118.8486   $118.85   $118.85   $118.80  
  7 purchase totals = $980.23       $1,060.9503   $1,060.96   $1,060.95   $1,061.00