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 $63.93   6.604%   $68.1519   $68.15   $68.15   $68.20  
  Purchase #2 $181.61   13.413%   $205.9693   $205.97   $205.95   $206.00  
  Purchase #3 $72.43   13.215%   $82.0016   $82.00   $82.00   $82.00  
  Purchase #4 $171.97   5.509%   $181.4438   $181.44   $181.45   $181.40  
  Purchase #5 $206.62   10.430%   $228.1705   $228.17   $228.15   $228.20  
  Purchase #6 $166.37   6.529%   $177.2323   $177.23   $177.25   $177.20  
  Purchase #7 $175.66   4.202%   $183.0412   $183.04   $183.05   $183.00  
  7 purchase totals = $1,038.59       $1,126.0106   $1,126.00   $1,126.00   $1,126.00