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 $62.74   6.773%   $66.9894   $66.99   $67.00   $67.00  
  Purchase #2 $167.86   10.617%   $185.6817   $185.68   $185.70   $185.70  
  Purchase #3 $176.95   12.206%   $198.5485   $198.55   $198.55   $198.50  
  Purchase #4 $12.41   13.619%   $14.1001   $14.10   $14.10   $14.10  
  Purchase #5 $149.72   13.465%   $169.8798   $169.88   $169.90   $169.90  
  Purchase #6 $229.56   4.231%   $239.2727   $239.27   $239.25   $239.30  
  Purchase #7 $9.65   3.460%   $9.9839   $9.98   $10.00   $10.00  
  7 purchase totals = $808.89       $884.4561   $884.45   $884.50   $884.50