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 $85.67   13.158%   $96.9425   $96.94   $96.95   $96.90  
  Purchase #2 $67.59   9.142%   $73.7691   $73.77   $73.75   $73.80  
  Purchase #3 $181.71   6.323%   $193.1995   $193.20   $193.20   $193.20  
  Purchase #4 $195.71   13.853%   $222.8217   $222.82   $222.80   $222.80  
  Purchase #5 $30.34   4.304%   $31.6458   $31.65   $31.65   $31.60  
  Purchase #6 $155.28   3.200%   $160.249   $160.25   $160.25   $160.20  
  Purchase #7 $113.61   3.828%   $117.959   $117.96   $117.95   $118.00  
  7 purchase totals = $829.91       $896.5866   $896.59   $896.55   $896.50