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 $140.87   7.198%   $151.0098   $151.01   $151.00   $151.00  
  Purchase #2 $62.43   9.674%   $68.4695   $68.47   $68.45   $68.50  
  Purchase #3 $69.74   13.278%   $79.0001   $79.00   $79.00   $79.00  
  Purchase #4 $52.38   4.535%   $54.7554   $54.76   $54.75   $54.80  
  Purchase #5 $151.61   13.185%   $171.5998   $171.60   $171.60   $171.60  
  Purchase #6 $120.81   13.328%   $136.9116   $136.91   $136.90   $136.90  
  Purchase #7 $202.83   6.839%   $216.7015   $216.70   $216.70   $216.70  
  7 purchase totals = $800.67       $878.4477   $878.45   $878.40   $878.50