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 $9.45   5.496%   $9.9694   $9.97   $9.95   $10.00  
  Purchase #2 $129.89   7.842%   $140.076   $140.08   $140.10   $140.10  
  Purchase #3 $30.31   7.624%   $32.6208   $32.62   $32.60   $32.60  
  Purchase #4 $177.51   10.276%   $195.7509   $195.75   $195.75   $195.80  
  Purchase #5 $208.38   5.591%   $220.0305   $220.03   $220.05   $220.00  
  Purchase #6 $114.83   3.113%   $118.4047   $118.40   $118.40   $118.40  
  Purchase #7 $166.99   8.835%   $181.7436   $181.74   $181.75   $181.70  
  7 purchase totals = $837.36       $898.5959   $898.59   $898.60   $898.60