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 $96.86   7.273%   $103.9046   $103.90   $103.90   $103.90  
  Purchase #2 $173.30   10.748%   $191.9263   $191.93   $191.95   $191.90  
  Purchase #3 $182.88   7.778%   $197.1044   $197.10   $197.10   $197.10  
  Purchase #4 $53.66   13.840%   $61.0865   $61.09   $61.10   $61.10  
  Purchase #5 $206.82   6.673%   $220.6211   $220.62   $220.60   $220.60  
  Purchase #6 $203.56   4.874%   $213.4815   $213.48   $213.50   $213.50  
  Purchase #7 $214.55   9.385%   $234.6855   $234.69   $234.70   $234.70  
  7 purchase totals = $1,131.63       $1,222.8099   $1,222.81   $1,222.85   $1,222.80