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 $67.68   8.242%   $73.2582   $73.26   $73.25   $73.30  
  Purchase #2 $72.37   3.146%   $74.6468   $74.65   $74.65   $74.60  
  Purchase #3 $55.70   9.264%   $60.86   $60.86   $60.85   $60.90  
  Purchase #4 $53.49   11.141%   $59.4493   $59.45   $59.45   $59.40  
  Purchase #5 $197.53   7.345%   $212.0386   $212.04   $212.05   $212.00  
  Purchase #6 $127.73   9.111%   $139.3675   $139.37   $139.35   $139.40  
  Purchase #7 $105.69   8.432%   $114.6018   $114.60   $114.60   $114.60  
  7 purchase totals = $680.19       $734.2222   $734.23   $734.20   $734.20