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 $200.42   11.779%   $224.0275   $224.03   $224.05   $224.00  
  Purchase #2 $77.93   9.345%   $85.2126   $85.21   $85.20   $85.20  
  Purchase #3 $165.30   6.656%   $176.3024   $176.30   $176.30   $176.30  
  Purchase #4 $187.32   10.543%   $207.0691   $207.07   $207.05   $207.10  
  Purchase #5 $90.69   13.162%   $102.6266   $102.63   $102.65   $102.60  
  Purchase #6 $229.36   10.424%   $253.2685   $253.27   $253.25   $253.30  
  Purchase #7 $34.35   7.393%   $36.8895   $36.89   $36.90   $36.90  
  7 purchase totals = $985.37       $1,085.3962   $1,085.40   $1,085.40   $1,085.40