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 $208.47   12.640%   $234.8206   $234.82   $234.80   $234.80  
  Purchase #2 $18.98   7.400%   $20.3845   $20.38   $20.40   $20.40  
  Purchase #3 $157.93   13.743%   $179.6343   $179.63   $179.65   $179.60  
  Purchase #4 $21.77   4.873%   $22.8309   $22.83   $22.85   $22.80  
  Purchase #5 $170.40   13.787%   $193.893   $193.89   $193.90   $193.90  
  Purchase #6 $49.43   12.682%   $55.6987   $55.70   $55.70   $55.70  
  Purchase #7 $52.44   7.128%   $56.1779   $56.18   $56.20   $56.20  
  7 purchase totals = $679.42       $763.4399   $763.43   $763.50   $763.40