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 $195.58   5.838%   $206.998   $207.00   $207.00   $207.00  
  Purchase #2 $84.56   6.151%   $89.7613   $89.76   $89.75   $89.80  
  Purchase #3 $195.58   11.474%   $218.0208   $218.02   $218.00   $218.00  
  Purchase #4 $68.84   12.556%   $77.4836   $77.48   $77.50   $77.50  
  Purchase #5 $89.32   7.859%   $96.3397   $96.34   $96.35   $96.30  
  Purchase #6 $39.68   5.235%   $41.7572   $41.76   $41.75   $41.80  
  Purchase #7 $109.79   8.544%   $119.1705   $119.17   $119.15   $119.20  
  7 purchase totals = $783.35       $849.5311   $849.53   $849.50   $849.60