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 $223.34   12.202%   $250.5919   $250.59   $250.60   $250.60  
  Purchase #2 $14.56   7.456%   $15.6456   $15.65   $15.65   $15.60  
  Purchase #3 $156.47   4.164%   $162.9854   $162.99   $163.00   $163.00  
  Purchase #4 $238.56   12.294%   $267.8886   $267.89   $267.90   $267.90  
  Purchase #5 $69.75   5.486%   $73.5765   $73.58   $73.60   $73.60  
  Purchase #6 $206.96   8.535%   $224.624   $224.62   $224.60   $224.60  
  Purchase #7 $158.76   7.490%   $170.6511   $170.65   $170.65   $170.70  
  7 purchase totals = $1,068.40       $1,165.9631   $1,165.97   $1,166.00   $1,166.00