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 $151.54   10.195%   $166.9895   $166.99   $167.00   $167.00  
  Purchase #2 $242.69   8.365%   $262.991   $262.99   $263.00   $263.00  
  Purchase #3 $64.88   6.687%   $69.2185   $69.22   $69.20   $69.20  
  Purchase #4 $244.96   6.248%   $260.2651   $260.27   $260.25   $260.30  
  Purchase #5 $55.69   9.156%   $60.789   $60.79   $60.80   $60.80  
  Purchase #6 $232.71   11.198%   $258.7689   $258.77   $258.75   $258.80  
  Purchase #7 $148.33   8.861%   $161.4735   $161.47   $161.45   $161.50  
  7 purchase totals = $1,140.80       $1,240.4955   $1,240.50   $1,240.45   $1,240.60