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 $205.49   8.806%   $223.5854   $223.59   $223.60   $223.60  
  Purchase #2 $92.78   6.655%   $98.9545   $98.95   $98.95   $99.00  
  Purchase #3 $239.68   10.200%   $264.1274   $264.13   $264.15   $264.10  
  Purchase #4 $117.25   11.670%   $130.9331   $130.93   $130.95   $130.90  
  Purchase #5 $162.40   8.874%   $176.8114   $176.81   $176.80   $176.80  
  Purchase #6 $52.77   11.612%   $58.8977   $58.90   $58.90   $58.90  
  Purchase #7 $162.94   8.215%   $176.3255   $176.33   $176.35   $176.30  
  7 purchase totals = $1,033.31       $1,129.6350   $1,129.64   $1,129.70   $1,129.60