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 $231.92   5.137%   $243.8337   $243.83   $243.85   $243.80  
  Purchase #2 $52.63   13.521%   $59.7461   $59.75   $59.75   $59.70  
  Purchase #3 $176.51   12.507%   $198.5861   $198.59   $198.60   $198.60  
  Purchase #4 $117.49   4.708%   $123.0214   $123.02   $123.00   $123.00  
  Purchase #5 $186.48   13.153%   $211.0077   $211.01   $211.00   $211.00  
  Purchase #6 $234.44   6.190%   $248.9518   $248.95   $248.95   $249.00  
  Purchase #7 $69.76   4.191%   $72.6836   $72.68   $72.70   $72.70  
  7 purchase totals = $1,069.23       $1,157.8304   $1,157.83   $1,157.85   $1,157.80