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 $212.61   11.284%   $236.6009   $236.60   $236.60   $236.60  
  Purchase #2 $71.31   3.361%   $73.7067   $73.71   $73.70   $73.70  
  Purchase #3 $247.51   3.397%   $255.9179   $255.92   $255.90   $255.90  
  Purchase #4 $19.38   3.739%   $20.1046   $20.10   $20.10   $20.10  
  Purchase #5 $64.28   13.604%   $73.0247   $73.02   $73.00   $73.00  
  Purchase #6 $27.51   10.239%   $30.3267   $30.33   $30.35   $30.30  
  Purchase #7 $52.67   5.180%   $55.3983   $55.40   $55.40   $55.40  
  7 purchase totals = $695.27       $745.0798   $745.08   $745.05   $745.00