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 $69.62   9.869%   $76.4908   $76.49   $76.50   $76.50  
  Purchase #2 $250.73   9.489%   $274.5218   $274.52   $274.50   $274.50  
  Purchase #3 $199.93   7.505%   $214.9347   $214.93   $214.95   $214.90  
  Purchase #4 $47.58   6.769%   $50.8007   $50.80   $50.80   $50.80  
  Purchase #5 $225.39   11.340%   $250.9492   $250.95   $250.95   $250.90  
  Purchase #6 $231.67   8.808%   $252.0755   $252.08   $252.10   $252.10  
  Purchase #7 $168.39   10.745%   $186.4835   $186.48   $186.50   $186.50  
  7 purchase totals = $1,193.31       $1,306.2562   $1,306.25   $1,306.30   $1,306.20