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 $216.98   13.456%   $246.1768   $246.18   $246.20   $246.20  
  Purchase #2 $227.98   9.140%   $248.8174   $248.82   $248.80   $248.80  
  Purchase #3 $30.54   8.737%   $33.2083   $33.21   $33.20   $33.20  
  Purchase #4 $225.91   3.416%   $233.6271   $233.63   $233.65   $233.60  
  Purchase #5 $54.85   3.805%   $56.937   $56.94   $56.95   $56.90  
  Purchase #6 $99.75   12.308%   $112.0272   $112.03   $112.05   $112.00  
  Purchase #7 $82.97   7.587%   $89.2649   $89.26   $89.25   $89.30  
  7 purchase totals = $938.98       $1,020.0587   $1,020.07   $1,020.10   $1,020.00