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 $187.97   8.380%   $203.7219   $203.72   $203.70   $203.70  
  Purchase #2 $70.66   3.768%   $73.3225   $73.32   $73.30   $73.30  
  Purchase #3 $223.64   13.572%   $253.9924   $253.99   $254.00   $254.00  
  Purchase #4 $105.60   8.278%   $114.3416   $114.34   $114.35   $114.30  
  Purchase #5 $241.86   9.694%   $265.3059   $265.31   $265.30   $265.30  
  Purchase #6 $46.29   7.253%   $49.6474   $49.65   $49.65   $49.60  
  Purchase #7 $105.68   8.190%   $114.3352   $114.34   $114.35   $114.30  
  7 purchase totals = $981.70       $1,074.6669   $1,074.67   $1,074.65   $1,074.50