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 $188.87   13.626%   $214.6054   $214.61   $214.60   $214.60  
  Purchase #2 $144.96   3.283%   $149.719   $149.72   $149.70   $149.70  
  Purchase #3 $60.65   8.783%   $65.9769   $65.98   $66.00   $66.00  
  Purchase #4 $22.67   3.708%   $23.5106   $23.51   $23.50   $23.50  
  Purchase #5 $92.56   12.757%   $104.3679   $104.37   $104.35   $104.40  
  Purchase #6 $61.81   11.419%   $68.8681   $68.87   $68.85   $68.90  
  Purchase #7 $51.37   8.855%   $55.9188   $55.92   $55.90   $55.90  
  7 purchase totals = $622.89       $682.9667   $682.98   $682.90   $683.00