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 $73.30   9.739%   $80.4387   $80.44   $80.45   $80.40  
  Purchase #2 $98.37   6.509%   $104.7729   $104.77   $104.75   $104.80  
  Purchase #3 $71.26   5.108%   $74.9   $74.90   $74.90   $74.90  
  Purchase #4 $182.87   8.515%   $198.4414   $198.44   $198.45   $198.40  
  Purchase #5 $240.53   10.337%   $265.3936   $265.39   $265.40   $265.40  
  Purchase #6 $97.59   8.694%   $106.0745   $106.07   $106.05   $106.10  
  Purchase #7 $177.65   10.421%   $196.1629   $196.16   $196.15   $196.20  
  7 purchase totals = $941.57       $1,026.1840   $1,026.17   $1,026.15   $1,026.20