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 $86.99   8.364%   $94.2658   $94.27   $94.25   $94.30  
  Purchase #2 $248.51   11.290%   $276.5668   $276.57   $276.55   $276.60  
  Purchase #3 $225.94   8.514%   $245.1765   $245.18   $245.20   $245.20  
  Purchase #4 $122.75   5.332%   $129.295   $129.30   $129.30   $129.30  
  Purchase #5 $118.64   11.564%   $132.3595   $132.36   $132.35   $132.40  
  Purchase #6 $230.60   4.386%   $240.7141   $240.71   $240.70   $240.70  
  Purchase #7 $202.39   11.500%   $225.6649   $225.66   $225.65   $225.70  
  7 purchase totals = $1,235.82       $1,344.0426   $1,344.05   $1,344.00   $1,344.20