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 $39.26   10.236%   $43.2787   $43.28   $43.30   $43.30  
  Purchase #2 $240.60   11.438%   $268.1198   $268.12   $268.10   $268.10  
  Purchase #3 $99.72   7.158%   $106.858   $106.86   $106.85   $106.90  
  Purchase #4 $34.59   6.569%   $36.8622   $36.86   $36.85   $36.90  
  Purchase #5 $165.71   11.272%   $184.3888   $184.39   $184.40   $184.40  
  Purchase #6 $42.78   8.656%   $46.483   $46.48   $46.50   $46.50  
  Purchase #7 $166.80   3.790%   $173.1217   $173.12   $173.10   $173.10  
  7 purchase totals = $789.46       $859.1122   $859.11   $859.10   $859.20