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 $246.64   9.318%   $269.6219   $269.62   $269.60   $269.60  
  Purchase #2 $191.82   4.164%   $199.8074   $199.81   $199.80   $199.80  
  Purchase #3 $214.97   13.555%   $244.1092   $244.11   $244.10   $244.10  
  Purchase #4 $88.45   13.411%   $100.312   $100.31   $100.30   $100.30  
  Purchase #5 $174.95   8.215%   $189.3221   $189.32   $189.30   $189.30  
  Purchase #6 $70.42   11.207%   $78.312   $78.31   $78.30   $78.30  
  Purchase #7 $114.73   4.527%   $119.9238   $119.92   $119.90   $119.90  
  7 purchase totals = $1,101.98       $1,201.4084   $1,201.40   $1,201.30   $1,201.30