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 $70.45   6.509%   $75.0356   $75.04   $75.05   $75.00  
  Purchase #2 $158.87   5.314%   $167.3124   $167.31   $167.30   $167.30  
  Purchase #3 $195.58   5.284%   $205.9144   $205.91   $205.90   $205.90  
  Purchase #4 $47.46   7.275%   $50.9127   $50.91   $50.90   $50.90  
  Purchase #5 $225.42   6.409%   $239.8672   $239.87   $239.85   $239.90  
  Purchase #6 $241.86   3.621%   $250.6178   $250.62   $250.60   $250.60  
  Purchase #7 $185.27   10.551%   $204.8178   $204.82   $204.80   $204.80  
  7 purchase totals = $1,124.91       $1,194.4779   $1,194.48   $1,194.40   $1,194.40