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 $152.97   5.647%   $161.6082   $161.61   $161.60   $161.60  
  Purchase #2 $20.67   9.244%   $22.5807   $22.58   $22.60   $22.60  
  Purchase #3 $15.97   4.563%   $16.6987   $16.70   $16.70   $16.70  
  Purchase #4 $41.43   9.379%   $45.3157   $45.32   $45.30   $45.30  
  Purchase #5 $225.37   6.254%   $239.4646   $239.46   $239.45   $239.50  
  Purchase #6 $33.34   4.712%   $34.911   $34.91   $34.90   $34.90  
  Purchase #7 $87.48   5.638%   $92.4121   $92.41   $92.40   $92.40  
  7 purchase totals = $577.23       $612.9910   $612.99   $612.95   $613.00