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 $63.70   10.524%   $70.4038   $70.40   $70.40   $70.40  
  Purchase #2 $181.57   6.819%   $193.9513   $193.95   $193.95   $194.00  
  Purchase #3 $240.82   13.720%   $273.8605   $273.86   $273.85   $273.90  
  Purchase #4 $146.74   10.811%   $162.6041   $162.60   $162.60   $162.60  
  Purchase #5 $124.75   4.810%   $130.7505   $130.75   $130.75   $130.80  
  Purchase #6 $247.81   5.794%   $262.1681   $262.17   $262.15   $262.20  
  Purchase #7 $95.45   12.416%   $107.3011   $107.30   $107.30   $107.30  
  7 purchase totals = $1,100.84       $1,201.0394   $1,201.03   $1,201.00   $1,201.20