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 $54.94   3.317%   $56.7624   $56.76   $56.75   $56.80  
  Purchase #2 $196.56   4.858%   $206.1089   $206.11   $206.10   $206.10  
  Purchase #3 $25.49   12.267%   $28.6169   $28.62   $28.60   $28.60  
  Purchase #4 $77.98   9.306%   $85.2368   $85.24   $85.25   $85.20  
  Purchase #5 $198.70   7.177%   $212.9607   $212.96   $212.95   $213.00  
  Purchase #6 $116.78   7.345%   $125.3575   $125.36   $125.35   $125.40  
  Purchase #7 $119.70   5.251%   $125.9854   $125.99   $126.00   $126.00  
  7 purchase totals = $790.15       $841.0286   $841.04   $841.00   $841.10