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 $35.53   3.244%   $36.6826   $36.68   $36.70   $36.70  
  Purchase #2 $250.62   8.225%   $271.2335   $271.23   $271.25   $271.20  
  Purchase #3 $236.63   3.568%   $245.073   $245.07   $245.05   $245.10  
  Purchase #4 $48.49   11.227%   $53.934   $53.93   $53.95   $53.90  
  Purchase #5 $227.47   4.728%   $238.2248   $238.22   $238.20   $238.20  
  Purchase #6 $250.94   12.383%   $282.0139   $282.01   $282.00   $282.00  
  Purchase #7 $128.60   5.517%   $135.6949   $135.69   $135.70   $135.70  
  7 purchase totals = $1,178.28       $1,262.8567   $1,262.83   $1,262.85   $1,262.80