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 $29.63   11.448%   $33.022   $33.02   $33.00   $33.00  
  Purchase #2 $237.71   7.695%   $256.0018   $256.00   $256.00   $256.00  
  Purchase #3 $156.76   7.156%   $167.9777   $167.98   $168.00   $168.00  
  Purchase #4 $211.59   8.422%   $229.4101   $229.41   $229.40   $229.40  
  Purchase #5 $178.44   10.303%   $196.8247   $196.82   $196.80   $196.80  
  Purchase #6 $60.48   12.579%   $68.0878   $68.09   $68.10   $68.10  
  Purchase #7 $248.88   6.250%   $264.435   $264.44   $264.45   $264.40  
  7 purchase totals = $1,123.49       $1,215.7591   $1,215.76   $1,215.75   $1,215.70