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 $63.45   12.112%   $71.1351   $71.14   $71.15   $71.10  
  Purchase #2 $165.50   13.326%   $187.5545   $187.55   $187.55   $187.60  
  Purchase #3 $36.71   5.429%   $38.703   $38.70   $38.70   $38.70  
  Purchase #4 $201.42   6.835%   $215.1871   $215.19   $215.20   $215.20  
  Purchase #5 $116.32   6.725%   $124.1425   $124.14   $124.15   $124.10  
  Purchase #6 $144.38   12.298%   $162.1359   $162.14   $162.15   $162.10  
  Purchase #7 $239.26   10.519%   $264.4278   $264.43   $264.45   $264.40  
  7 purchase totals = $967.04       $1,063.2859   $1,063.29   $1,063.35   $1,063.20