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 $113.47   5.153%   $119.3171   $119.32   $119.30   $119.30  
  Purchase #2 $229.63   3.579%   $237.8485   $237.85   $237.85   $237.80  
  Purchase #3 $185.79   3.751%   $192.759   $192.76   $192.75   $192.80  
  Purchase #4 $145.36   6.138%   $154.2822   $154.28   $154.30   $154.30  
  Purchase #5 $59.62   4.284%   $62.1741   $62.17   $62.15   $62.20  
  Purchase #6 $32.83   11.388%   $36.5687   $36.57   $36.55   $36.60  
  Purchase #7 $11.27   3.807%   $11.699   $11.70   $11.70   $11.70  
  7 purchase totals = $777.97       $814.6486   $814.65   $814.60   $814.70