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 $84.49   12.475%   $95.0301   $95.03   $95.05   $95.00  
  Purchase #2 $101.68   12.628%   $114.5202   $114.52   $114.50   $114.50  
  Purchase #3 $167.70   10.437%   $185.2028   $185.20   $185.20   $185.20  
  Purchase #4 $47.99   12.444%   $53.9619   $53.96   $53.95   $54.00  
  Purchase #5 $55.62   12.797%   $62.7377   $62.74   $62.75   $62.70  
  Purchase #6 $158.85   9.193%   $173.4531   $173.45   $173.45   $173.50  
  Purchase #7 $132.75   8.704%   $144.3046   $144.30   $144.30   $144.30  
  7 purchase totals = $749.08       $829.2104   $829.20   $829.20   $829.20