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 $187.58   6.374%   $199.5363   $199.54   $199.55   $199.50  
  Purchase #2 $91.99   4.809%   $96.4138   $96.41   $96.40   $96.40  
  Purchase #3 $227.32   11.114%   $252.5843   $252.58   $252.60   $252.60  
  Purchase #4 $131.34   9.150%   $143.3576   $143.36   $143.35   $143.40  
  Purchase #5 $101.44   12.860%   $114.4852   $114.49   $114.50   $114.50  
  Purchase #6 $154.65   11.283%   $172.0992   $172.10   $172.10   $172.10  
  Purchase #7 $163.40   12.564%   $183.9296   $183.93   $183.95   $183.90  
  7 purchase totals = $1,057.72       $1,162.4060   $1,162.41   $1,162.45   $1,162.40