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 $125.49   13.427%   $142.3395   $142.34   $142.35   $142.30  
  Purchase #2 $147.76   12.259%   $165.8739   $165.87   $165.85   $165.90  
  Purchase #3 $196.29   3.502%   $203.1641   $203.16   $203.15   $203.20  
  Purchase #4 $31.91   8.809%   $34.721   $34.72   $34.70   $34.70  
  Purchase #5 $87.27   9.383%   $95.4585   $95.46   $95.45   $95.50  
  Purchase #6 $227.26   6.240%   $241.441   $241.44   $241.45   $241.40  
  Purchase #7 $107.48   6.272%   $114.2211   $114.22   $114.20   $114.20  
  7 purchase totals = $923.46       $997.2191   $997.21   $997.15   $997.20