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 $61.80   11.789%   $69.0856   $69.09   $69.10   $69.10  
  Purchase #2 $231.30   6.584%   $246.5288   $246.53   $246.55   $246.50  
  Purchase #3 $69.37   12.355%   $77.9407   $77.94   $77.95   $77.90  
  Purchase #4 $65.92   10.601%   $72.9082   $72.91   $72.90   $72.90  
  Purchase #5 $84.30   13.372%   $95.5726   $95.57   $95.55   $95.60  
  Purchase #6 $171.57   3.539%   $177.6419   $177.64   $177.65   $177.60  
  Purchase #7 $194.72   10.696%   $215.5473   $215.55   $215.55   $215.50  
  7 purchase totals = $878.98       $955.2251   $955.23   $955.25   $955.10