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 $61.99   12.398%   $69.6755   $69.68   $69.70   $69.70  
  Purchase #2 $17.28   9.637%   $18.9453   $18.95   $18.95   $18.90  
  Purchase #3 $58.99   9.607%   $64.6572   $64.66   $64.65   $64.70  
  Purchase #4 $246.29   10.660%   $272.5445   $272.54   $272.55   $272.50  
  Purchase #5 $153.60   13.746%   $174.7139   $174.71   $174.70   $174.70  
  Purchase #6 $61.54   7.135%   $65.9309   $65.93   $65.95   $65.90  
  Purchase #7 $42.48   11.570%   $47.3949   $47.39   $47.40   $47.40  
  7 purchase totals = $642.17       $713.8622   $713.86   $713.90   $713.80