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 $204.36   6.327%   $217.2899   $217.29   $217.30   $217.30  
  Purchase #2 $111.74   4.114%   $116.337   $116.34   $116.35   $116.30  
  Purchase #3 $33.47   11.559%   $37.3388   $37.34   $37.35   $37.30  
  Purchase #4 $187.25   12.263%   $210.2125   $210.21   $210.20   $210.20  
  Purchase #5 $248.88   7.146%   $266.665   $266.67   $266.65   $266.70  
  Purchase #6 $54.41   3.246%   $56.1761   $56.18   $56.20   $56.20  
  Purchase #7 $95.91   13.267%   $108.6344   $108.63   $108.65   $108.60  
  7 purchase totals = $936.02       $1,012.6537   $1,012.66   $1,012.70   $1,012.60