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 $30.91   6.606%   $32.9519   $32.95   $32.95   $33.00  
  Purchase #2 $22.49   6.531%   $23.9588   $23.96   $23.95   $24.00  
  Purchase #3 $69.65   4.755%   $72.9619   $72.96   $72.95   $73.00  
  Purchase #4 $40.30   10.444%   $44.5089   $44.51   $44.50   $44.50  
  Purchase #5 $213.42   11.772%   $238.5438   $238.54   $238.55   $238.50  
  Purchase #6 $201.52   12.662%   $227.0365   $227.04   $227.05   $227.00  
  Purchase #7 $103.89   8.420%   $112.6375   $112.64   $112.65   $112.60  
  7 purchase totals = $682.18       $752.5993   $752.60   $752.60   $752.60