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 $92.61   6.457%   $98.5898   $98.59   $98.60   $98.60  
  Purchase #2 $115.61   4.429%   $120.7304   $120.73   $120.75   $120.70  
  Purchase #3 $181.26   5.483%   $191.1985   $191.20   $191.20   $191.20  
  Purchase #4 $214.86   3.433%   $222.2361   $222.24   $222.25   $222.20  
  Purchase #5 $190.91   5.530%   $201.4673   $201.47   $201.45   $201.50  
  Purchase #6 $83.77   5.451%   $88.3363   $88.34   $88.35   $88.30  
  Purchase #7 $11.30   5.403%   $11.9105   $11.91   $11.90   $11.90  
  7 purchase totals = $890.32       $934.4689   $934.48   $934.50   $934.40