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 $11.84   11.797%   $13.2368   $13.24   $13.25   $13.20  
  Purchase #2 $62.74   12.188%   $70.3868   $70.39   $70.40   $70.40  
  Purchase #3 $27.46   12.689%   $30.9444   $30.94   $30.95   $30.90  
  Purchase #4 $248.91   3.206%   $256.8901   $256.89   $256.90   $256.90  
  Purchase #5 $212.88   7.289%   $228.3968   $228.40   $228.40   $228.40  
  Purchase #6 $172.88   7.813%   $186.3871   $186.39   $186.40   $186.40  
  Purchase #7 $226.30   10.649%   $250.3987   $250.40   $250.40   $250.40  
  7 purchase totals = $963.01       $1,036.6407   $1,036.65   $1,036.70   $1,036.60