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 $209.93   10.443%   $231.853   $231.85   $231.85   $231.90  
  Purchase #2 $42.56   9.689%   $46.6836   $46.68   $46.70   $46.70  
  Purchase #3 $34.58   6.305%   $36.7603   $36.76   $36.75   $36.80  
  Purchase #4 $125.76   13.853%   $143.1815   $143.18   $143.20   $143.20  
  Purchase #5 $178.92   9.553%   $196.0122   $196.01   $196.00   $196.00  
  Purchase #6 $50.29   6.320%   $53.4683   $53.47   $53.45   $53.50  
  Purchase #7 $240.76   4.623%   $251.8903   $251.89   $251.90   $251.90  
  7 purchase totals = $882.80       $959.8492   $959.84   $959.85   $960.00