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 $219.70   6.217%   $233.3587   $233.36   $233.35   $233.40  
  Purchase #2 $98.93   4.554%   $103.4353   $103.44   $103.45   $103.40  
  Purchase #3 $22.60   3.211%   $23.3257   $23.33   $23.35   $23.30  
  Purchase #4 $212.64   3.869%   $220.867   $220.87   $220.85   $220.90  
  Purchase #5 $218.72   8.335%   $236.9503   $236.95   $236.95   $237.00  
  Purchase #6 $44.35   6.593%   $47.274   $47.27   $47.25   $47.30  
  Purchase #7 $180.31   8.166%   $195.0341   $195.03   $195.05   $195.00  
  7 purchase totals = $997.25       $1,060.2451   $1,060.25   $1,060.25   $1,060.30