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 $177.74   10.251%   $195.9601   $195.96   $195.95   $196.00  
  Purchase #2 $50.84   3.333%   $52.5345   $52.53   $52.55   $52.50  
  Purchase #3 $146.86   4.764%   $153.8564   $153.86   $153.85   $153.90  
  Purchase #4 $38.79   8.125%   $41.9417   $41.94   $41.95   $41.90  
  Purchase #5 $69.63   6.819%   $74.3781   $74.38   $74.40   $74.40  
  Purchase #6 $125.74   12.176%   $141.0501   $141.05   $141.05   $141.10  
  Purchase #7 $119.70   12.642%   $134.8325   $134.83   $134.85   $134.80  
  7 purchase totals = $729.30       $794.5534   $794.55   $794.60   $794.60