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 $39.31   13.578%   $44.6475   $44.65   $44.65   $44.60  
  Purchase #2 $127.78   12.568%   $143.8394   $143.84   $143.85   $143.80  
  Purchase #3 $42.86   8.758%   $46.6137   $46.61   $46.60   $46.60  
  Purchase #4 $216.54   5.478%   $228.4021   $228.40   $228.40   $228.40  
  Purchase #5 $167.93   10.371%   $185.346   $185.35   $185.35   $185.30  
  Purchase #6 $16.35   11.560%   $18.2401   $18.24   $18.25   $18.20  
  Purchase #7 $84.74   8.781%   $92.181   $92.18   $92.20   $92.20  
  7 purchase totals = $695.51       $759.2698   $759.27   $759.30   $759.10