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 $34.62   8.506%   $37.5648   $37.56   $37.55   $37.60  
  Purchase #2 $230.87   12.465%   $259.6479   $259.65   $259.65   $259.60  
  Purchase #3 $158.59   6.419%   $168.7699   $168.77   $168.75   $168.80  
  Purchase #4 $193.76   12.492%   $217.9645   $217.96   $217.95   $218.00  
  Purchase #5 $129.64   8.794%   $141.0405   $141.04   $141.05   $141.00  
  Purchase #6 $16.66   8.530%   $18.0811   $18.08   $18.10   $18.10  
  Purchase #7 $103.70   12.705%   $116.8751   $116.88   $116.90   $116.90  
  7 purchase totals = $867.84       $959.9438   $959.94   $959.95   $960.00