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 $193.74   13.541%   $219.9743   $219.97   $219.95   $220.00  
  Purchase #2 $76.34   12.634%   $85.9848   $85.98   $86.00   $86.00  
  Purchase #3 $31.99   12.655%   $36.0383   $36.04   $36.05   $36.00  
  Purchase #4 $68.42   3.662%   $70.9255   $70.93   $70.95   $70.90  
  Purchase #5 $214.51   5.814%   $226.9816   $226.98   $227.00   $227.00  
  Purchase #6 $247.45   11.555%   $276.0428   $276.04   $276.05   $276.00  
  Purchase #7 $23.93   10.473%   $26.4362   $26.44   $26.45   $26.40  
  7 purchase totals = $856.38       $942.3835   $942.38   $942.45   $942.30