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 $40.81   9.126%   $44.5343   $44.53   $44.55   $44.50  
  Purchase #2 $107.89   10.588%   $119.3134   $119.31   $119.30   $119.30  
  Purchase #3 $53.95   11.846%   $60.3409   $60.34   $60.35   $60.30  
  Purchase #4 $225.27   10.309%   $248.4931   $248.49   $248.50   $248.50  
  Purchase #5 $76.77   5.306%   $80.8434   $80.84   $80.85   $80.80  
  Purchase #6 $214.95   9.186%   $234.6953   $234.70   $234.70   $234.70  
  Purchase #7 $27.41   6.765%   $29.2643   $29.26   $29.25   $29.30  
  7 purchase totals = $747.05       $817.4847   $817.47   $817.50   $817.40