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 $62.41   10.252%   $68.8083   $68.81   $68.80   $68.80  
  Purchase #2 $201.51   10.584%   $222.8378   $222.84   $222.85   $222.80  
  Purchase #3 $225.33   11.458%   $251.1483   $251.15   $251.15   $251.10  
  Purchase #4 $11.82   10.775%   $13.0936   $13.09   $13.10   $13.10  
  Purchase #5 $177.82   7.375%   $190.9342   $190.93   $190.95   $190.90  
  Purchase #6 $123.61   7.309%   $132.6447   $132.64   $132.65   $132.60  
  Purchase #7 $78.40   7.509%   $84.2871   $84.29   $84.30   $84.30  
  7 purchase totals = $880.90       $963.7540   $963.75   $963.80   $963.60