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 $57.80   8.703%   $62.8303   $62.83   $62.85   $62.80  
  Purchase #2 $153.90   10.161%   $169.5378   $169.54   $169.55   $169.50  
  Purchase #3 $221.51   3.714%   $229.7369   $229.74   $229.75   $229.70  
  Purchase #4 $76.40   11.814%   $85.4259   $85.43   $85.45   $85.40  
  Purchase #5 $151.58   7.848%   $163.476   $163.48   $163.50   $163.50  
  Purchase #6 $165.70   11.714%   $185.1101   $185.11   $185.10   $185.10  
  Purchase #7 $101.33   9.136%   $110.5875   $110.59   $110.60   $110.60  
  7 purchase totals = $928.22       $1,006.7045   $1,006.72   $1,006.80   $1,006.60