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 $196.54   12.761%   $221.6205   $221.62   $221.60   $221.60  
  Purchase #2 $189.90   6.739%   $202.6974   $202.70   $202.70   $202.70  
  Purchase #3 $163.53   4.820%   $171.4121   $171.41   $171.40   $171.40  
  Purchase #4 $181.50   6.593%   $193.4663   $193.47   $193.45   $193.50  
  Purchase #5 $206.88   7.105%   $221.5788   $221.58   $221.60   $221.60  
  Purchase #6 $70.53   6.582%   $75.1723   $75.17   $75.15   $75.20  
  Purchase #7 $195.59   6.440%   $208.186   $208.19   $208.20   $208.20  
  7 purchase totals = $1,204.47       $1,294.1334   $1,294.14   $1,294.10   $1,294.20