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 $56.29   10.291%   $62.0828   $62.08   $62.10   $62.10  
  Purchase #2 $228.82   9.722%   $251.0659   $251.07   $251.05   $251.10  
  Purchase #3 $165.90   11.774%   $185.4331   $185.43   $185.45   $185.40  
  Purchase #4 $162.30   13.316%   $183.9119   $183.91   $183.90   $183.90  
  Purchase #5 $159.40   10.770%   $176.5674   $176.57   $176.55   $176.60  
  Purchase #6 $101.61   12.527%   $114.3387   $114.34   $114.35   $114.30  
  Purchase #7 $84.32   9.190%   $92.069   $92.07   $92.05   $92.10  
  7 purchase totals = $958.64       $1,065.4688   $1,065.47   $1,065.45   $1,065.50