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 $246.27   8.109%   $266.24   $266.24   $266.25   $266.20  
  Purchase #2 $85.91   6.756%   $91.7141   $91.71   $91.70   $91.70  
  Purchase #3 $109.61   3.110%   $113.0189   $113.02   $113.00   $113.00  
  Purchase #4 $219.52   5.673%   $231.9734   $231.97   $231.95   $232.00  
  Purchase #5 $67.99   4.416%   $70.9924   $70.99   $71.00   $71.00  
  Purchase #6 $84.40   8.738%   $91.7749   $91.77   $91.75   $91.80  
  Purchase #7 $79.75   8.196%   $86.2863   $86.29   $86.30   $86.30  
  7 purchase totals = $893.45       $952.0000   $951.99   $951.95   $952.00