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 $175.27   9.656%   $192.1941   $192.19   $192.20   $192.20  
  Purchase #2 $95.76   3.373%   $98.99   $98.99   $99.00   $99.00  
  Purchase #3 $181.42   3.445%   $187.6699   $187.67   $187.65   $187.70  
  Purchase #4 $23.92   11.449%   $26.6586   $26.66   $26.65   $26.70  
  Purchase #5 $40.69   4.162%   $42.3835   $42.38   $42.40   $42.40  
  Purchase #6 $246.83   6.641%   $263.222   $263.22   $263.20   $263.20  
  Purchase #7 $24.32   11.260%   $27.0584   $27.06   $27.05   $27.10  
  7 purchase totals = $788.21       $838.1765   $838.17   $838.15   $838.30