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 $56.25   11.839%   $62.9094   $62.91   $62.90   $62.90  
  Purchase #2 $218.60   13.154%   $247.3546   $247.35   $247.35   $247.40  
  Purchase #3 $56.33   13.326%   $63.8365   $63.84   $63.85   $63.80  
  Purchase #4 $215.89   3.751%   $223.988   $223.99   $224.00   $224.00  
  Purchase #5 $88.68   4.433%   $92.6112   $92.61   $92.60   $92.60  
  Purchase #6 $109.63   8.768%   $119.2424   $119.24   $119.25   $119.20  
  Purchase #7 $120.49   9.460%   $131.8884   $131.89   $131.90   $131.90  
  7 purchase totals = $865.87       $941.8305   $941.83   $941.85   $941.80