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 $55.30   13.127%   $62.5592   $62.56   $62.55   $62.60  
  Purchase #2 $167.43   4.116%   $174.3214   $174.32   $174.30   $174.30  
  Purchase #3 $250.99   3.672%   $260.2064   $260.21   $260.20   $260.20  
  Purchase #4 $234.82   5.461%   $247.6435   $247.64   $247.65   $247.60  
  Purchase #5 $232.48   5.628%   $245.564   $245.56   $245.55   $245.60  
  Purchase #6 $118.32   7.291%   $126.9467   $126.95   $126.95   $126.90  
  Purchase #7 $140.43   8.704%   $152.653   $152.65   $152.65   $152.70  
  7 purchase totals = $1,199.77       $1,269.8942   $1,269.89   $1,269.85   $1,269.90