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 $95.55   3.173%   $98.5818   $98.58   $98.60   $98.60  
  Purchase #2 $189.51   4.818%   $198.6406   $198.64   $198.65   $198.60  
  Purchase #3 $175.43   12.521%   $197.3956   $197.40   $197.40   $197.40  
  Purchase #4 $45.38   10.324%   $50.065   $50.07   $50.05   $50.10  
  Purchase #5 $120.26   5.752%   $127.1774   $127.18   $127.20   $127.20  
  Purchase #6 $205.55   6.477%   $218.8635   $218.86   $218.85   $218.90  
  Purchase #7 $165.31   4.150%   $172.1704   $172.17   $172.15   $172.20  
  7 purchase totals = $996.99       $1,062.8943   $1,062.90   $1,062.90   $1,063.00