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 $246.92   7.163%   $264.6069   $264.61   $264.60   $264.60  
  Purchase #2 $123.68   12.670%   $139.3503   $139.35   $139.35   $139.40  
  Purchase #3 $8.52   4.685%   $8.9192   $8.92   $8.90   $8.90  
  Purchase #4 $166.77   12.588%   $187.763   $187.76   $187.75   $187.80  
  Purchase #5 $123.78   12.639%   $139.4246   $139.42   $139.40   $139.40  
  Purchase #6 $85.59   9.510%   $93.7296   $93.73   $93.75   $93.70  
  Purchase #7 $184.28   8.515%   $199.9714   $199.97   $199.95   $200.00  
  7 purchase totals = $939.54       $1,033.7650   $1,033.76   $1,033.70   $1,033.80