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 $63.86   10.746%   $70.7224   $70.72   $70.70   $70.70  
  Purchase #2 $70.81   6.131%   $75.1514   $75.15   $75.15   $75.20  
  Purchase #3 $124.37   4.434%   $129.8846   $129.88   $129.90   $129.90  
  Purchase #4 $28.67   6.829%   $30.6279   $30.63   $30.65   $30.60  
  Purchase #5 $211.82   6.135%   $224.8152   $224.82   $224.80   $224.80  
  Purchase #6 $164.26   13.470%   $186.3858   $186.39   $186.40   $186.40  
  Purchase #7 $7.99   6.184%   $8.4841   $8.48   $8.50   $8.50  
  7 purchase totals = $671.78       $726.0714   $726.07   $726.10   $726.10