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 $52.99   7.844%   $57.1465   $57.15   $57.15   $57.10  
  Purchase #2 $92.71   5.389%   $97.7061   $97.71   $97.70   $97.70  
  Purchase #3 $68.79   13.769%   $78.2617   $78.26   $78.25   $78.30  
  Purchase #4 $83.34   13.606%   $94.6792   $94.68   $94.70   $94.70  
  Purchase #5 $12.76   12.303%   $14.3299   $14.33   $14.35   $14.30  
  Purchase #6 $230.47   13.787%   $262.2449   $262.24   $262.25   $262.20  
  Purchase #7 $246.48   8.559%   $267.5762   $267.58   $267.60   $267.60  
  7 purchase totals = $787.54       $871.9445   $871.95   $872.00   $871.90