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 $88.79   7.732%   $95.6552   $95.66   $95.65   $95.70  
  Purchase #2 $207.94   4.107%   $216.4801   $216.48   $216.50   $216.50  
  Purchase #3 $62.31   4.603%   $65.1781   $65.18   $65.20   $65.20  
  Purchase #4 $26.53   4.187%   $27.6408   $27.64   $27.65   $27.60  
  Purchase #5 $34.29   7.871%   $36.989   $36.99   $37.00   $37.00  
  Purchase #6 $19.63   9.722%   $21.5384   $21.54   $21.55   $21.50  
  Purchase #7 $242.85   13.859%   $276.5066   $276.51   $276.50   $276.50  
  7 purchase totals = $682.34       $739.9882   $740.00   $740.05   $740.00