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 $59.27   5.751%   $62.6786   $62.68   $62.70   $62.70  
  Purchase #2 $201.86   12.573%   $227.2399   $227.24   $227.25   $227.20  
  Purchase #3 $71.79   3.543%   $74.3335   $74.33   $74.35   $74.30  
  Purchase #4 $68.65   11.152%   $76.3058   $76.31   $76.30   $76.30  
  Purchase #5 $89.86   11.408%   $100.1112   $100.11   $100.10   $100.10  
  Purchase #6 $151.59   4.126%   $157.8446   $157.84   $157.85   $157.80  
  Purchase #7 $204.67   4.781%   $214.4553   $214.46   $214.45   $214.50  
  7 purchase totals = $847.69       $912.9689   $912.97   $913.00   $912.90