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 $22.77   9.640%   $24.965   $24.97   $24.95   $25.00  
  Purchase #2 $202.29   7.190%   $216.8347   $216.83   $216.85   $216.80  
  Purchase #3 $88.45   7.382%   $94.9794   $94.98   $95.00   $95.00  
  Purchase #4 $68.32   8.203%   $73.9243   $73.92   $73.90   $73.90  
  Purchase #5 $128.77   9.647%   $141.1924   $141.19   $141.20   $141.20  
  Purchase #6 $246.61   5.249%   $259.5546   $259.55   $259.55   $259.60  
  Purchase #7 $151.90   3.827%   $157.7132   $157.71   $157.70   $157.70  
  7 purchase totals = $909.11       $969.1636   $969.15   $969.15   $969.20