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 $28.31   13.176%   $32.0401   $32.04   $32.05   $32.00  
  Purchase #2 $159.61   10.813%   $176.8686   $176.87   $176.85   $176.90  
  Purchase #3 $208.84   5.819%   $220.9924   $220.99   $221.00   $221.00  
  Purchase #4 $107.36   8.688%   $116.6874   $116.69   $116.70   $116.70  
  Purchase #5 $177.93   9.592%   $194.997   $195.00   $195.00   $195.00  
  Purchase #6 $103.29   7.696%   $111.2392   $111.24   $111.25   $111.20  
  Purchase #7 $188.36   10.438%   $208.021   $208.02   $208.00   $208.00  
  7 purchase totals = $973.70       $1,060.8457   $1,060.85   $1,060.85   $1,060.80