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 $84.39   9.613%   $92.5024   $92.50   $92.50   $92.50  
  Purchase #2 $248.55   5.807%   $262.9833   $262.98   $263.00   $263.00  
  Purchase #3 $166.45   9.873%   $182.8836   $182.88   $182.90   $182.90  
  Purchase #4 $88.62   11.307%   $98.6403   $98.64   $98.65   $98.60  
  Purchase #5 $17.34   12.755%   $19.5517   $19.55   $19.55   $19.60  
  Purchase #6 $194.41   5.559%   $205.2173   $205.22   $205.20   $205.20  
  Purchase #7 $195.89   7.766%   $211.1028   $211.10   $211.10   $211.10  
  7 purchase totals = $995.65       $1,072.8814   $1,072.87   $1,072.90   $1,072.90