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 $87.56   10.397%   $96.6636   $96.66   $96.65   $96.70  
  Purchase #2 $102.92   10.428%   $113.6525   $113.65   $113.65   $113.70  
  Purchase #3 $27.27   7.284%   $29.2563   $29.26   $29.25   $29.30  
  Purchase #4 $153.85   11.207%   $171.092   $171.09   $171.10   $171.10  
  Purchase #5 $95.89   7.693%   $103.2668   $103.27   $103.25   $103.30  
  Purchase #6 $114.77   13.874%   $130.6932   $130.69   $130.70   $130.70  
  Purchase #7 $201.94   13.357%   $228.9131   $228.91   $228.90   $228.90  
  7 purchase totals = $784.20       $873.5375   $873.53   $873.50   $873.70