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 $157.92   11.811%   $176.5719   $176.57   $176.55   $176.60  
  Purchase #2 $187.78   5.408%   $197.9351   $197.94   $197.95   $197.90  
  Purchase #3 $178.77   7.630%   $192.4102   $192.41   $192.40   $192.40  
  Purchase #4 $191.70   6.273%   $203.7253   $203.73   $203.75   $203.70  
  Purchase #5 $174.89   12.386%   $196.5519   $196.55   $196.55   $196.60  
  Purchase #6 $232.45   13.439%   $263.689   $263.69   $263.70   $263.70  
  Purchase #7 $16.60   12.662%   $18.7019   $18.70   $18.70   $18.70  
  7 purchase totals = $1,140.11       $1,249.5853   $1,249.59   $1,249.60   $1,249.60