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 $211.70   4.759%   $221.7748   $221.77   $221.75   $221.80  
  Purchase #2 $48.46   11.571%   $54.0673   $54.07   $54.05   $54.10  
  Purchase #3 $24.29   4.661%   $25.4222   $25.42   $25.40   $25.40  
  Purchase #4 $48.35   5.850%   $51.1785   $51.18   $51.20   $51.20  
  Purchase #5 $195.77   5.365%   $206.2731   $206.27   $206.25   $206.30  
  Purchase #6 $5.27   3.382%   $5.4482   $5.45   $5.45   $5.40  
  Purchase #7 $30.89   5.481%   $32.5831   $32.58   $32.60   $32.60  
  7 purchase totals = $564.73       $596.7472   $596.74   $596.70   $596.80