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 $170.72   13.658%   $194.0369   $194.04   $194.05   $194.00  
  Purchase #2 $180.81   12.288%   $203.0279   $203.03   $203.05   $203.00  
  Purchase #3 $185.47   5.383%   $195.4539   $195.45   $195.45   $195.50  
  Purchase #4 $56.31   3.528%   $58.2966   $58.30   $58.30   $58.30  
  Purchase #5 $70.64   7.631%   $76.0305   $76.03   $76.05   $76.00  
  Purchase #6 $216.50   11.266%   $240.8909   $240.89   $240.90   $240.90  
  Purchase #7 $231.58   9.611%   $253.8372   $253.84   $253.85   $253.80  
  7 purchase totals = $1,112.03       $1,221.5739   $1,221.58   $1,221.65   $1,221.50