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 $53.31   8.788%   $57.9949   $57.99   $58.00   $58.00  
  Purchase #2 $243.43   13.212%   $275.592   $275.59   $275.60   $275.60  
  Purchase #3 $129.87   9.770%   $142.5583   $142.56   $142.55   $142.60  
  Purchase #4 $205.66   13.258%   $232.9264   $232.93   $232.95   $232.90  
  Purchase #5 $153.36   9.497%   $167.9246   $167.92   $167.90   $167.90  
  Purchase #6 $249.91   4.555%   $261.2934   $261.29   $261.30   $261.30  
  Purchase #7 $120.75   10.293%   $133.1788   $133.18   $133.20   $133.20  
  7 purchase totals = $1,156.29       $1,271.4684   $1,271.46   $1,271.50   $1,271.50