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 $197.76   13.265%   $223.9929   $223.99   $224.00   $224.00  
  Purchase #2 $47.99   9.310%   $52.4579   $52.46   $52.45   $52.50  
  Purchase #3 $20.85   8.865%   $22.6984   $22.70   $22.70   $22.70  
  Purchase #4 $159.32   5.430%   $167.9711   $167.97   $167.95   $168.00  
  Purchase #5 $191.85   13.220%   $217.2126   $217.21   $217.20   $217.20  
  Purchase #6 $73.28   13.436%   $83.1259   $83.13   $83.15   $83.10  
  Purchase #7 $245.73   11.483%   $273.9472   $273.95   $273.95   $273.90  
  7 purchase totals = $936.78       $1,041.4060   $1,041.41   $1,041.40   $1,041.40