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 $57.96   5.199%   $60.9733   $60.97   $60.95   $61.00  
  Purchase #2 $119.81   10.516%   $132.4092   $132.41   $132.40   $132.40  
  Purchase #3 $160.99   5.767%   $170.2743   $170.27   $170.25   $170.30  
  Purchase #4 $11.89   13.309%   $13.4724   $13.47   $13.45   $13.50  
  Purchase #5 $112.93   10.516%   $124.8057   $124.81   $124.80   $124.80  
  Purchase #6 $8.55   13.235%   $9.6816   $9.68   $9.70   $9.70  
  Purchase #7 $86.86   12.440%   $97.6654   $97.67   $97.65   $97.70  
  7 purchase totals = $558.99       $609.2819   $609.28   $609.20   $609.40