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 $146.72   13.837%   $167.0216   $167.02   $167.00   $167.00  
  Purchase #2 $232.26   13.341%   $263.2458   $263.25   $263.25   $263.20  
  Purchase #3 $168.43   8.233%   $182.2968   $182.30   $182.30   $182.30  
  Purchase #4 $124.63   13.430%   $141.3678   $141.37   $141.35   $141.40  
  Purchase #5 $171.96   8.378%   $186.3668   $186.37   $186.35   $186.40  
  Purchase #6 $9.25   8.778%   $10.062   $10.06   $10.05   $10.10  
  Purchase #7 $241.86   12.433%   $271.9305   $271.93   $271.95   $271.90  
  7 purchase totals = $1,095.11       $1,222.2913   $1,222.30   $1,222.25   $1,222.30