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 $181.72   6.590%   $193.6953   $193.70   $193.70   $193.70  
  Purchase #2 $214.47   8.859%   $233.4699   $233.47   $233.45   $233.50  
  Purchase #3 $135.94   11.362%   $151.3855   $151.39   $151.40   $151.40  
  Purchase #4 $143.27   4.630%   $149.9034   $149.90   $149.90   $149.90  
  Purchase #5 $72.83   3.217%   $75.1729   $75.17   $75.15   $75.20  
  Purchase #6 $232.29   3.156%   $239.6211   $239.62   $239.60   $239.60  
  Purchase #7 $192.51   12.568%   $216.7047   $216.70   $216.70   $216.70  
  7 purchase totals = $1,173.03       $1,259.9528   $1,259.95   $1,259.90   $1,260.00