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 $196.52   6.854%   $209.9895   $209.99   $210.00   $210.00  
  Purchase #2 $129.83   4.769%   $136.0216   $136.02   $136.00   $136.00  
  Purchase #3 $188.35   8.264%   $203.9152   $203.92   $203.90   $203.90  
  Purchase #4 $119.36   9.122%   $130.248   $130.25   $130.25   $130.20  
  Purchase #5 $48.56   11.109%   $53.9545   $53.95   $53.95   $54.00  
  Purchase #6 $140.33   5.559%   $148.1309   $148.13   $148.15   $148.10  
  Purchase #7 $132.84   13.759%   $151.1175   $151.12   $151.10   $151.10  
  7 purchase totals = $955.79       $1,033.3772   $1,033.38   $1,033.35   $1,033.30