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 $55.47   10.468%   $61.2766   $61.28   $61.30   $61.30  
  Purchase #2 $200.91   5.843%   $212.6492   $212.65   $212.65   $212.60  
  Purchase #3 $137.79   7.638%   $148.3144   $148.31   $148.30   $148.30  
  Purchase #4 $127.84   4.318%   $133.3601   $133.36   $133.35   $133.40  
  Purchase #5 $51.95   10.363%   $57.3336   $57.33   $57.35   $57.30  
  Purchase #6 $32.74   8.449%   $35.5062   $35.51   $35.50   $35.50  
  Purchase #7 $57.30   13.742%   $65.1742   $65.17   $65.15   $65.20  
  7 purchase totals = $664.00       $713.6143   $713.61   $713.60   $713.60