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 $235.52   12.776%   $265.61   $265.61   $265.60   $265.60  
  Purchase #2 $247.82   9.729%   $271.9304   $271.93   $271.95   $271.90  
  Purchase #3 $131.68   4.260%   $137.2896   $137.29   $137.30   $137.30  
  Purchase #4 $231.34   13.262%   $262.0203   $262.02   $262.00   $262.00  
  Purchase #5 $69.81   6.385%   $74.2674   $74.27   $74.25   $74.30  
  Purchase #6 $166.32   8.552%   $180.5437   $180.54   $180.55   $180.50  
  Purchase #7 $249.80   11.423%   $278.3347   $278.33   $278.35   $278.30  
  7 purchase totals = $1,332.29       $1,469.9961   $1,469.99   $1,470.00   $1,469.90