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 $181.53   4.251%   $189.2468   $189.25   $189.25   $189.20  
  Purchase #2 $13.68   4.865%   $14.3455   $14.35   $14.35   $14.30  
  Purchase #3 $151.51   7.195%   $162.4111   $162.41   $162.40   $162.40  
  Purchase #4 $164.35   6.485%   $175.0081   $175.01   $175.00   $175.00  
  Purchase #5 $58.96   8.418%   $63.9233   $63.92   $63.90   $63.90  
  Purchase #6 $237.54   11.120%   $263.9544   $263.95   $263.95   $264.00  
  Purchase #7 $62.68   10.784%   $69.4394   $69.44   $69.45   $69.40  
  7 purchase totals = $870.25       $938.3286   $938.33   $938.30   $938.20