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 $111.47   13.685%   $126.7247   $126.72   $126.70   $126.70  
  Purchase #2 $41.57   8.674%   $45.1758   $45.18   $45.20   $45.20  
  Purchase #3 $5.49   10.229%   $6.0516   $6.05   $6.05   $6.10  
  Purchase #4 $184.82   3.487%   $191.2647   $191.26   $191.25   $191.30  
  Purchase #5 $88.46   11.201%   $98.3684   $98.37   $98.35   $98.40  
  Purchase #6 $147.57   4.564%   $154.3051   $154.31   $154.30   $154.30  
  Purchase #7 $121.63   13.208%   $137.6949   $137.69   $137.70   $137.70  
  7 purchase totals = $701.01       $759.5852   $759.58   $759.55   $759.70