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 $64.73   13.666%   $73.576   $73.58   $73.60   $73.60  
  Purchase #2 $205.80   4.253%   $214.5527   $214.55   $214.55   $214.60  
  Purchase #3 $43.26   7.229%   $46.3873   $46.39   $46.40   $46.40  
  Purchase #4 $89.27   3.467%   $92.365   $92.37   $92.35   $92.40  
  Purchase #5 $53.70   5.447%   $56.625   $56.63   $56.65   $56.60  
  Purchase #6 $37.72   10.727%   $41.7662   $41.77   $41.75   $41.80  
  Purchase #7 $245.34   3.655%   $254.3072   $254.31   $254.30   $254.30  
  7 purchase totals = $739.82       $779.5794   $779.60   $779.60   $779.70