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 $184.76   13.391%   $209.5012   $209.50   $209.50   $209.50  
  Purchase #2 $116.27   13.383%   $131.8304   $131.83   $131.85   $131.80  
  Purchase #3 $74.86   8.356%   $81.1153   $81.12   $81.10   $81.10  
  Purchase #4 $235.73   13.231%   $266.9194   $266.92   $266.90   $266.90  
  Purchase #5 $56.77   6.129%   $60.2494   $60.25   $60.25   $60.20  
  Purchase #6 $226.79   3.253%   $234.1675   $234.17   $234.15   $234.20  
  Purchase #7 $132.93   13.180%   $150.4502   $150.45   $150.45   $150.50  
  7 purchase totals = $1,028.11       $1,134.2334   $1,134.24   $1,134.20   $1,134.20