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 $211.62   9.392%   $231.4954   $231.50   $231.50   $231.50  
  Purchase #2 $168.51   11.609%   $188.0723   $188.07   $188.05   $188.10  
  Purchase #3 $110.54   11.495%   $123.2466   $123.25   $123.25   $123.20  
  Purchase #4 $63.92   4.153%   $66.5746   $66.57   $66.55   $66.60  
  Purchase #5 $191.72   3.135%   $197.7304   $197.73   $197.75   $197.70  
  Purchase #6 $38.69   9.278%   $42.2797   $42.28   $42.30   $42.30  
  Purchase #7 $167.66   11.572%   $187.0616   $187.06   $187.05   $187.10  
  7 purchase totals = $952.66       $1,036.4606   $1,036.46   $1,036.45   $1,036.50