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 $65.62   5.446%   $69.1937   $69.19   $69.20   $69.20  
  Purchase #2 $68.28   13.804%   $77.7054   $77.71   $77.70   $77.70  
  Purchase #3 $56.79   9.278%   $62.059   $62.06   $62.05   $62.10  
  Purchase #4 $179.31   11.121%   $199.2511   $199.25   $199.25   $199.30  
  Purchase #5 $190.98   12.452%   $214.7608   $214.76   $214.75   $214.80  
  Purchase #6 $119.79   11.524%   $133.5946   $133.59   $133.60   $133.60  
  Purchase #7 $224.73   9.852%   $246.8704   $246.87   $246.85   $246.90  
  7 purchase totals = $905.50       $1,003.4350   $1,003.43   $1,003.40   $1,003.60