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 $59.32   13.370%   $67.2511   $67.25   $67.25   $67.30  
  Purchase #2 $153.82   9.551%   $168.5113   $168.51   $168.50   $168.50  
  Purchase #3 $186.68   6.141%   $198.144   $198.14   $198.15   $198.10  
  Purchase #4 $119.31   9.736%   $130.926   $130.93   $130.95   $130.90  
  Purchase #5 $169.99   9.673%   $186.4331   $186.43   $186.45   $186.40  
  Purchase #6 $205.71   10.337%   $226.9742   $226.97   $226.95   $227.00  
  Purchase #7 $124.33   13.742%   $141.4154   $141.42   $141.40   $141.40  
  7 purchase totals = $1,019.16       $1,119.6551   $1,119.65   $1,119.65   $1,119.60