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 $184.74   8.773%   $200.9472   $200.95   $200.95   $200.90  
  Purchase #2 $148.43   6.207%   $157.6431   $157.64   $157.65   $157.60  
  Purchase #3 $223.94   11.354%   $249.3661   $249.37   $249.35   $249.40  
  Purchase #4 $55.46   3.439%   $57.3673   $57.37   $57.35   $57.40  
  Purchase #5 $241.85   10.848%   $268.0859   $268.09   $268.10   $268.10  
  Purchase #6 $227.91   10.812%   $252.5516   $252.55   $252.55   $252.60  
  Purchase #7 $172.66   4.643%   $180.6766   $180.68   $180.70   $180.70  
  7 purchase totals = $1,254.99       $1,366.6378   $1,366.65   $1,366.65   $1,366.70