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 $163.69   3.266%   $169.0361   $169.04   $169.05   $169.00  
  Purchase #2 $21.57   11.338%   $24.0156   $24.02   $24.00   $24.00  
  Purchase #3 $175.26   4.176%   $182.5789   $182.58   $182.60   $182.60  
  Purchase #4 $187.27   10.344%   $206.6412   $206.64   $206.65   $206.60  
  Purchase #5 $178.28   8.365%   $193.1931   $193.19   $193.20   $193.20  
  Purchase #6 $54.50   3.725%   $56.5301   $56.53   $56.55   $56.50  
  Purchase #7 $151.81   11.614%   $169.4412   $169.44   $169.45   $169.40  
  7 purchase totals = $932.38       $1,001.4362   $1,001.44   $1,001.50   $1,001.30