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 $55.87   8.103%   $60.3971   $60.40   $60.40   $60.40  
  Purchase #2 $178.44   10.313%   $196.8425   $196.84   $196.85   $196.80  
  Purchase #3 $229.60   6.807%   $245.2289   $245.23   $245.25   $245.20  
  Purchase #4 $171.47   9.113%   $187.0961   $187.10   $187.10   $187.10  
  Purchase #5 $214.42   10.299%   $236.5031   $236.50   $236.50   $236.50  
  Purchase #6 $181.84   9.425%   $198.9784   $198.98   $199.00   $199.00  
  Purchase #7 $22.38   11.722%   $25.0034   $25.00   $25.00   $25.00  
  7 purchase totals = $1,054.02       $1,150.0495   $1,150.05   $1,150.10   $1,150.00