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 $238.26   4.216%   $248.305   $248.31   $248.30   $248.30  
  Purchase #2 $119.35   11.155%   $132.6635   $132.66   $132.65   $132.70  
  Purchase #3 $61.75   7.439%   $66.3436   $66.34   $66.35   $66.30  
  Purchase #4 $149.25   12.536%   $167.96   $167.96   $167.95   $168.00  
  Purchase #5 $7.71   8.166%   $8.3396   $8.34   $8.35   $8.30  
  Purchase #6 $94.95   9.810%   $104.2646   $104.26   $104.25   $104.30  
  Purchase #7 $227.84   5.209%   $239.7082   $239.71   $239.70   $239.70  
  7 purchase totals = $899.11       $967.5845   $967.58   $967.55   $967.60