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 $232.72   11.188%   $258.7567   $258.76   $258.75   $258.80  
  Purchase #2 $237.47   13.449%   $269.4073   $269.41   $269.40   $269.40  
  Purchase #3 $58.37   11.159%   $64.8835   $64.88   $64.90   $64.90  
  Purchase #4 $95.28   4.333%   $99.4085   $99.41   $99.40   $99.40  
  Purchase #5 $37.46   5.291%   $39.442   $39.44   $39.45   $39.40  
  Purchase #6 $106.88   8.469%   $115.9317   $115.93   $115.95   $115.90  
  Purchase #7 $246.74   11.443%   $274.9745   $274.97   $274.95   $275.00  
  7 purchase totals = $1,014.92       $1,122.8042   $1,122.80   $1,122.80   $1,122.80