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 $149.36   13.486%   $169.5027   $169.50   $169.50   $169.50  
  Purchase #2 $245.86   10.218%   $270.982   $270.98   $271.00   $271.00  
  Purchase #3 $244.71   6.149%   $259.7572   $259.76   $259.75   $259.80  
  Purchase #4 $117.88   7.758%   $127.0251   $127.03   $127.05   $127.00  
  Purchase #5 $75.44   11.445%   $84.0741   $84.07   $84.05   $84.10  
  Purchase #6 $87.42   9.444%   $95.6759   $95.68   $95.70   $95.70  
  Purchase #7 $15.38   8.189%   $16.6395   $16.64   $16.65   $16.60  
  7 purchase totals = $936.05       $1,023.6565   $1,023.66   $1,023.70   $1,023.70