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 $109.56   3.181%   $113.0451   $113.05   $113.05   $113.00  
  Purchase #2 $65.53   11.354%   $72.9703   $72.97   $72.95   $73.00  
  Purchase #3 $11.37   4.722%   $11.9069   $11.91   $11.90   $11.90  
  Purchase #4 $82.89   3.139%   $85.4919   $85.49   $85.50   $85.50  
  Purchase #5 $248.65   9.534%   $272.3563   $272.36   $272.35   $272.40  
  Purchase #6 $31.90   4.393%   $33.3014   $33.30   $33.30   $33.30  
  Purchase #7 $153.95   10.797%   $170.572   $170.57   $170.55   $170.60  
  7 purchase totals = $703.85       $759.6439   $759.65   $759.60   $759.70