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 $232.51   7.143%   $249.1182   $249.12   $249.10   $249.10  
  Purchase #2 $94.50   4.297%   $98.5607   $98.56   $98.55   $98.60  
  Purchase #3 $112.45   10.727%   $124.5125   $124.51   $124.50   $124.50  
  Purchase #4 $152.86   9.294%   $167.0668   $167.07   $167.05   $167.10  
  Purchase #5 $69.46   6.527%   $73.9937   $73.99   $74.00   $74.00  
  Purchase #6 $79.36   11.624%   $88.5848   $88.58   $88.60   $88.60  
  Purchase #7 $139.57   3.238%   $144.0893   $144.09   $144.10   $144.10  
  7 purchase totals = $880.71       $945.9260   $945.92   $945.90   $946.00