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 $247.91   13.740%   $281.9728   $281.97   $281.95   $282.00  
  Purchase #2 $205.78   4.496%   $215.0319   $215.03   $215.05   $215.00  
  Purchase #3 $66.61   10.366%   $73.5148   $73.51   $73.50   $73.50  
  Purchase #4 $5.74   9.218%   $6.2691   $6.27   $6.25   $6.30  
  Purchase #5 $250.91   9.600%   $274.9974   $275.00   $275.00   $275.00  
  Purchase #6 $168.91   12.874%   $190.6555   $190.66   $190.65   $190.70  
  Purchase #7 $224.39   3.180%   $231.5256   $231.53   $231.55   $231.50  
  7 purchase totals = $1,170.25       $1,273.9671   $1,273.97   $1,273.95   $1,274.00