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 $211.67   7.578%   $227.7104   $227.71   $227.70   $227.70  
  Purchase #2 $64.83   3.208%   $66.9097   $66.91   $66.90   $66.90  
  Purchase #3 $151.26   11.542%   $168.7184   $168.72   $168.70   $168.70  
  Purchase #4 $33.30   9.644%   $36.5115   $36.51   $36.50   $36.50  
  Purchase #5 $153.35   10.174%   $168.9518   $168.95   $168.95   $169.00  
  Purchase #6 $227.35   5.437%   $239.711   $239.71   $239.70   $239.70  
  Purchase #7 $184.75   7.799%   $199.1587   $199.16   $199.15   $199.20  
  7 purchase totals = $1,026.51       $1,107.6715   $1,107.67   $1,107.60   $1,107.70