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 $58.98   4.732%   $61.7709   $61.77   $61.75   $61.80  
  Purchase #2 $249.74   11.209%   $277.7334   $277.73   $277.75   $277.70  
  Purchase #3 $83.47   10.155%   $91.9464   $91.95   $91.95   $91.90  
  Purchase #4 $71.40   7.366%   $76.6593   $76.66   $76.65   $76.70  
  Purchase #5 $195.47   13.468%   $221.7959   $221.80   $221.80   $221.80  
  Purchase #6 $203.67   3.285%   $210.3606   $210.36   $210.35   $210.40  
  Purchase #7 $240.69   11.334%   $267.9698   $267.97   $267.95   $268.00  
  7 purchase totals = $1,103.42       $1,208.2363   $1,208.24   $1,208.20   $1,208.30