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 $209.81   8.306%   $227.2368   $227.24   $227.25   $227.20  
  Purchase #2 $67.38   11.775%   $75.314   $75.31   $75.30   $75.30  
  Purchase #3 $128.76   8.623%   $139.863   $139.86   $139.85   $139.90  
  Purchase #4 $109.36   8.474%   $118.6272   $118.63   $118.65   $118.60  
  Purchase #5 $136.99   4.762%   $143.5135   $143.51   $143.50   $143.50  
  Purchase #6 $108.52   11.185%   $120.658   $120.66   $120.65   $120.70  
  Purchase #7 $233.69   8.261%   $252.9951   $253.00   $253.00   $253.00  
  7 purchase totals = $994.51       $1,078.2076   $1,078.21   $1,078.20   $1,078.20