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 $60.76   8.773%   $66.0905   $66.09   $66.10   $66.10  
  Purchase #2 $176.94   8.535%   $192.0418   $192.04   $192.05   $192.00  
  Purchase #3 $39.34   6.418%   $41.8648   $41.86   $41.85   $41.90  
  Purchase #4 $221.40   9.464%   $242.3533   $242.35   $242.35   $242.40  
  Purchase #5 $169.62   8.806%   $184.5567   $184.56   $184.55   $184.60  
  Purchase #6 $191.58   12.716%   $215.9413   $215.94   $215.95   $215.90  
  Purchase #7 $97.48   10.496%   $107.7115   $107.71   $107.70   $107.70  
  7 purchase totals = $957.12       $1,050.5599   $1,050.55   $1,050.55   $1,050.60