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 $52.83   11.683%   $59.0021   $59.00   $59.00   $59.00  
  Purchase #2 $222.57   7.812%   $239.9572   $239.96   $239.95   $240.00  
  Purchase #3 $46.85   10.447%   $51.7444   $51.74   $51.75   $51.70  
  Purchase #4 $225.61   11.480%   $251.51   $251.51   $251.50   $251.50  
  Purchase #5 $81.80   8.674%   $88.8953   $88.90   $88.90   $88.90  
  Purchase #6 $241.44   4.578%   $252.4931   $252.49   $252.50   $252.50  
  Purchase #7 $245.55   5.747%   $259.6618   $259.66   $259.65   $259.70  
  7 purchase totals = $1,116.65       $1,203.2639   $1,203.26   $1,203.25   $1,203.30