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 $84.79   9.388%   $92.7501   $92.75   $92.75   $92.80  
  Purchase #2 $232.28   3.387%   $240.1473   $240.15   $240.15   $240.10  
  Purchase #3 $18.82   13.425%   $21.3466   $21.35   $21.35   $21.30  
  Purchase #4 $215.98   4.468%   $225.63   $225.63   $225.65   $225.60  
  Purchase #5 $133.27   6.874%   $142.431   $142.43   $142.45   $142.40  
  Purchase #6 $230.90   6.767%   $246.525   $246.53   $246.55   $246.50  
  Purchase #7 $221.93   10.732%   $245.7475   $245.75   $245.75   $245.70  
  7 purchase totals = $1,137.97       $1,214.5775   $1,214.59   $1,214.65   $1,214.40