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 $167.40   11.546%   $186.728   $186.73   $186.75   $186.70  
  Purchase #2 $44.49   7.647%   $47.8922   $47.89   $47.90   $47.90  
  Purchase #3 $189.61   13.173%   $214.5873   $214.59   $214.60   $214.60  
  Purchase #4 $216.45   3.803%   $224.6816   $224.68   $224.70   $224.70  
  Purchase #5 $122.93   12.104%   $137.8094   $137.81   $137.80   $137.80  
  Purchase #6 $147.71   6.328%   $157.0571   $157.06   $157.05   $157.10  
  Purchase #7 $32.86   9.456%   $35.9672   $35.97   $35.95   $36.00  
  7 purchase totals = $921.45       $1,004.7228   $1,004.73   $1,004.75   $1,004.80