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 $56.49   9.638%   $61.9345   $61.93   $61.95   $61.90  
  Purchase #2 $195.28   5.517%   $206.0536   $206.05   $206.05   $206.10  
  Purchase #3 $93.36   9.705%   $102.4206   $102.42   $102.40   $102.40  
  Purchase #4 $71.51   7.483%   $76.8611   $76.86   $76.85   $76.90  
  Purchase #5 $20.75   4.870%   $21.7605   $21.76   $21.75   $21.80  
  Purchase #6 $119.31   3.824%   $123.8724   $123.87   $123.85   $123.90  
  Purchase #7 $137.37   13.415%   $155.7982   $155.80   $155.80   $155.80  
  7 purchase totals = $694.07       $748.7009   $748.69   $748.65   $748.80