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 $68.76   7.309%   $73.7857   $73.79   $73.80   $73.80  
  Purchase #2 $245.87   12.613%   $276.8816   $276.88   $276.90   $276.90  
  Purchase #3 $232.28   12.109%   $260.4068   $260.41   $260.40   $260.40  
  Purchase #4 $49.92   11.584%   $55.7027   $55.70   $55.70   $55.70  
  Purchase #5 $109.51   3.364%   $113.1939   $113.19   $113.20   $113.20  
  Purchase #6 $238.66   4.694%   $249.8627   $249.86   $249.85   $249.90  
  Purchase #7 $121.51   10.771%   $134.5978   $134.60   $134.60   $134.60  
  7 purchase totals = $1,066.51       $1,164.4312   $1,164.43   $1,164.45   $1,164.50