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 $94.53   4.285%   $98.5806   $98.58   $98.60   $98.60  
  Purchase #2 $168.41   9.452%   $184.3281   $184.33   $184.35   $184.30  
  Purchase #3 $8.66   11.413%   $9.6484   $9.65   $9.65   $9.60  
  Purchase #4 $178.63   10.312%   $197.0503   $197.05   $197.05   $197.10  
  Purchase #5 $29.99   10.758%   $33.2163   $33.22   $33.20   $33.20  
  Purchase #6 $99.32   8.700%   $107.9608   $107.96   $107.95   $108.00  
  Purchase #7 $110.49   6.787%   $117.989   $117.99   $118.00   $118.00  
  7 purchase totals = $690.03       $748.7735   $748.78   $748.80   $748.80