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 $153.46   12.652%   $172.8758   $172.88   $172.90   $172.90  
  Purchase #2 $119.68   4.683%   $125.2846   $125.28   $125.30   $125.30  
  Purchase #3 $216.36   3.503%   $223.9391   $223.94   $223.95   $223.90  
  Purchase #4 $116.55   11.851%   $130.3623   $130.36   $130.35   $130.40  
  Purchase #5 $237.68   12.160%   $266.5819   $266.58   $266.60   $266.60  
  Purchase #6 $53.81   5.638%   $56.8438   $56.84   $56.85   $56.80  
  Purchase #7 $250.77   5.824%   $265.3748   $265.37   $265.35   $265.40  
  7 purchase totals = $1,148.31       $1,241.2623   $1,241.25   $1,241.30   $1,241.30