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 $54.35   9.831%   $59.6931   $59.69   $59.70   $59.70  
  Purchase #2 $125.29   6.589%   $133.5454   $133.55   $133.55   $133.50  
  Purchase #3 $67.74   3.217%   $69.9192   $69.92   $69.90   $69.90  
  Purchase #4 $69.84   8.645%   $75.8777   $75.88   $75.90   $75.90  
  Purchase #5 $63.91   4.113%   $66.5386   $66.54   $66.55   $66.50  
  Purchase #6 $193.53   3.667%   $200.6267   $200.63   $200.65   $200.60  
  Purchase #7 $115.88   7.175%   $124.1944   $124.19   $124.20   $124.20  
  7 purchase totals = $690.54       $730.3951   $730.40   $730.45   $730.30