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 $91.39   13.798%   $104   $104.00   $104.00   $104.00  
  Purchase #2 $44.39   3.105%   $45.7683   $45.77   $45.75   $45.80  
  Purchase #3 $55.59   8.280%   $60.1929   $60.19   $60.20   $60.20  
  Purchase #4 $218.60   10.476%   $241.5005   $241.50   $241.50   $241.50  
  Purchase #5 $199.62   5.533%   $210.665   $210.67   $210.65   $210.70  
  Purchase #6 $76.31   4.530%   $79.7668   $79.77   $79.75   $79.80  
  Purchase #7 $21.78   10.234%   $24.009   $24.01   $24.00   $24.00  
  7 purchase totals = $707.68       $765.9025   $765.91   $765.85   $766.00