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 $73.47   7.544%   $79.0126   $79.01   $79.00   $79.00  
  Purchase #2 $236.76   10.649%   $261.9726   $261.97   $261.95   $262.00  
  Purchase #3 $156.91   6.665%   $167.3681   $167.37   $167.35   $167.40  
  Purchase #4 $129.29   13.424%   $146.6459   $146.65   $146.65   $146.60  
  Purchase #5 $157.99   5.625%   $166.8769   $166.88   $166.90   $166.90  
  Purchase #6 $7.77   12.666%   $8.7541   $8.75   $8.75   $8.80  
  Purchase #7 $236.73   8.137%   $255.9927   $255.99   $256.00   $256.00  
  7 purchase totals = $998.92       $1,086.6229   $1,086.62   $1,086.60   $1,086.70