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 $95.94   3.823%   $99.6078   $99.61   $99.60   $99.60  
  Purchase #2 $169.46   8.382%   $183.6641   $183.66   $183.65   $183.70  
  Purchase #3 $241.88   3.632%   $250.6651   $250.67   $250.65   $250.70  
  Purchase #4 $73.63   8.854%   $80.1492   $80.15   $80.15   $80.10  
  Purchase #5 $203.90   5.115%   $214.3295   $214.33   $214.35   $214.30  
  Purchase #6 $196.27   5.477%   $207.0197   $207.02   $207.00   $207.00  
  Purchase #7 $28.41   3.621%   $29.4387   $29.44   $29.45   $29.40  
  7 purchase totals = $1,009.49       $1,064.8741   $1,064.88   $1,064.85   $1,064.80