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 $94.80   4.110%   $98.6963   $98.70   $98.70   $98.70  
  Purchase #2 $143.51   9.232%   $156.7588   $156.76   $156.75   $156.80  
  Purchase #3 $152.66   6.115%   $161.9952   $162.00   $162.00   $162.00  
  Purchase #4 $61.43   12.663%   $69.2089   $69.21   $69.20   $69.20  
  Purchase #5 $33.50   8.464%   $36.3354   $36.34   $36.35   $36.30  
  Purchase #6 $103.65   5.420%   $109.2678   $109.27   $109.25   $109.30  
  Purchase #7 $243.97   8.359%   $264.3635   $264.36   $264.35   $264.40  
  7 purchase totals = $833.52       $896.6259   $896.64   $896.60   $896.70