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 $164.74   13.411%   $186.8333   $186.83   $186.85   $186.80  
  Purchase #2 $94.47   9.388%   $103.3388   $103.34   $103.35   $103.30  
  Purchase #3 $244.65   11.399%   $272.5377   $272.54   $272.55   $272.50  
  Purchase #4 $73.54   4.237%   $76.6559   $76.66   $76.65   $76.70  
  Purchase #5 $22.99   6.787%   $24.5503   $24.55   $24.55   $24.60  
  Purchase #6 $135.67   6.644%   $144.6839   $144.68   $144.70   $144.70  
  Purchase #7 $88.95   13.230%   $100.7181   $100.72   $100.70   $100.70  
  7 purchase totals = $825.01       $909.3180   $909.32   $909.35   $909.30