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 $70.49   8.676%   $76.6057   $76.61   $76.60   $76.60  
  Purchase #2 $85.92   11.858%   $96.1084   $96.11   $96.10   $96.10  
  Purchase #3 $114.94   5.719%   $121.5134   $121.51   $121.50   $121.50  
  Purchase #4 $233.76   9.764%   $256.5843   $256.58   $256.60   $256.60  
  Purchase #5 $180.41   8.382%   $195.532   $195.53   $195.55   $195.50  
  Purchase #6 $6.42   11.405%   $7.1522   $7.15   $7.15   $7.20  
  Purchase #7 $101.87   4.855%   $106.8158   $106.82   $106.80   $106.80  
  7 purchase totals = $793.81       $860.3118   $860.31   $860.30   $860.30