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 $200.88   11.694%   $224.3709   $224.37   $224.35   $224.40  
  Purchase #2 $59.91   6.207%   $63.6286   $63.63   $63.65   $63.60  
  Purchase #3 $58.59   4.514%   $61.2348   $61.23   $61.25   $61.20  
  Purchase #4 $228.48   13.714%   $259.8137   $259.81   $259.80   $259.80  
  Purchase #5 $55.31   5.455%   $58.3272   $58.33   $58.35   $58.30  
  Purchase #6 $231.62   13.410%   $262.6802   $262.68   $262.70   $262.70  
  Purchase #7 $104.58   10.304%   $115.3559   $115.36   $115.35   $115.40  
  7 purchase totals = $939.37       $1,045.4113   $1,045.41   $1,045.45   $1,045.40