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 $67.66   12.493%   $76.1128   $76.11   $76.10   $76.10  
  Purchase #2 $230.69   8.716%   $250.7969   $250.80   $250.80   $250.80  
  Purchase #3 $207.99   12.805%   $234.6231   $234.62   $234.60   $234.60  
  Purchase #4 $109.79   7.784%   $118.3361   $118.34   $118.35   $118.30  
  Purchase #5 $225.90   12.272%   $253.6224   $253.62   $253.60   $253.60  
  Purchase #6 $236.53   6.625%   $252.2001   $252.20   $252.20   $252.20  
  Purchase #7 $168.41   11.204%   $187.2787   $187.28   $187.30   $187.30  
  7 purchase totals = $1,246.97       $1,372.9701   $1,372.97   $1,372.95   $1,372.90