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 $248.76   7.718%   $267.9593   $267.96   $267.95   $268.00  
  Purchase #2 $50.26   11.798%   $56.1897   $56.19   $56.20   $56.20  
  Purchase #3 $174.44   4.166%   $181.7072   $181.71   $181.70   $181.70  
  Purchase #4 $87.73   6.177%   $93.1491   $93.15   $93.15   $93.10  
  Purchase #5 $178.27   12.218%   $200.051   $200.05   $200.05   $200.10  
  Purchase #6 $32.76   6.365%   $34.8452   $34.85   $34.85   $34.80  
  Purchase #7 $181.90   3.259%   $187.8281   $187.83   $187.85   $187.80  
  7 purchase totals = $954.12       $1,021.7296   $1,021.74   $1,021.75   $1,021.70