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 $58.39   7.157%   $62.569   $62.57   $62.55   $62.60  
  Purchase #2 $74.34   10.209%   $81.9294   $81.93   $81.95   $81.90  
  Purchase #3 $68.39   6.666%   $72.9489   $72.95   $72.95   $72.90  
  Purchase #4 $177.95   9.685%   $195.1845   $195.18   $195.20   $195.20  
  Purchase #5 $164.54   5.117%   $172.9595   $172.96   $172.95   $173.00  
  Purchase #6 $61.85   4.539%   $64.6574   $64.66   $64.65   $64.70  
  Purchase #7 $198.34   5.641%   $209.5284   $209.53   $209.55   $209.50  
  7 purchase totals = $803.80       $859.7771   $859.78   $859.80   $859.80