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 $203.81   12.369%   $229.0193   $229.02   $229.00   $229.00  
  Purchase #2 $117.92   7.409%   $126.6567   $126.66   $126.65   $126.70  
  Purchase #3 $132.74   3.176%   $136.9558   $136.96   $136.95   $137.00  
  Purchase #4 $97.84   3.133%   $100.9053   $100.91   $100.90   $100.90  
  Purchase #5 $201.46   10.839%   $223.2962   $223.30   $223.30   $223.30  
  Purchase #6 $207.55   4.659%   $217.2198   $217.22   $217.20   $217.20  
  Purchase #7 $164.63   6.863%   $175.9286   $175.93   $175.95   $175.90  
  7 purchase totals = $1,125.95       $1,209.9817   $1,210.00   $1,209.95   $1,210.00