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 $227.89   8.160%   $246.4858   $246.49   $246.50   $246.50  
  Purchase #2 $225.37   6.491%   $239.9988   $240.00   $240.00   $240.00  
  Purchase #3 $196.33   8.512%   $213.0416   $213.04   $213.05   $213.00  
  Purchase #4 $81.51   12.698%   $91.8601   $91.86   $91.85   $91.90  
  Purchase #5 $7.86   6.235%   $8.3501   $8.35   $8.35   $8.40  
  Purchase #6 $171.44   4.554%   $179.2474   $179.25   $179.25   $179.20  
  Purchase #7 $239.34   7.552%   $257.415   $257.42   $257.40   $257.40  
  7 purchase totals = $1,149.74       $1,236.3988   $1,236.41   $1,236.40   $1,236.40