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 $52.76   13.266%   $59.7591   $59.76   $59.75   $59.80  
  Purchase #2 $140.84   5.204%   $148.1693   $148.17   $148.15   $148.20  
  Purchase #3 $83.95   4.517%   $87.742   $87.74   $87.75   $87.70  
  Purchase #4 $215.25   5.444%   $226.9682   $226.97   $226.95   $227.00  
  Purchase #5 $187.49   12.695%   $211.2919   $211.29   $211.30   $211.30  
  Purchase #6 $60.72   9.608%   $66.554   $66.55   $66.55   $66.60  
  Purchase #7 $5.68   3.859%   $5.8992   $5.90   $5.90   $5.90  
  7 purchase totals = $746.69       $806.3837   $806.38   $806.35   $806.50