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 $124.36   11.440%   $138.5868   $138.59   $138.60   $138.60  
  Purchase #2 $50.76   7.264%   $54.4472   $54.45   $54.45   $54.40  
  Purchase #3 $231.34   5.494%   $244.0498   $244.05   $244.05   $244.00  
  Purchase #4 $214.71   11.316%   $239.0066   $239.01   $239.00   $239.00  
  Purchase #5 $86.51   9.192%   $94.462   $94.46   $94.45   $94.50  
  Purchase #6 $17.59   3.338%   $18.1772   $18.18   $18.20   $18.20  
  Purchase #7 $235.63   11.278%   $262.2044   $262.20   $262.20   $262.20  
  7 purchase totals = $960.90       $1,050.9340   $1,050.94   $1,050.95   $1,050.90