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 $147.57   5.740%   $156.0405   $156.04   $156.05   $156.00  
  Purchase #2 $95.57   7.351%   $102.5954   $102.60   $102.60   $102.60  
  Purchase #3 $125.72   9.296%   $137.4069   $137.41   $137.40   $137.40  
  Purchase #4 $62.36   12.697%   $70.2778   $70.28   $70.30   $70.30  
  Purchase #5 $165.31   4.423%   $172.6217   $172.62   $172.60   $172.60  
  Purchase #6 $76.62   10.292%   $84.5057   $84.51   $84.50   $84.50  
  Purchase #7 $250.73   4.730%   $262.5895   $262.59   $262.60   $262.60  
  7 purchase totals = $923.88       $986.0375   $986.05   $986.05   $986.00