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 $44.44   5.316%   $46.8024   $46.80   $46.80   $46.80  
  Purchase #2 $248.53   8.266%   $269.0735   $269.07   $269.05   $269.10  
  Purchase #3 $170.83   4.426%   $178.3909   $178.39   $178.40   $178.40  
  Purchase #4 $61.57   5.110%   $64.7162   $64.72   $64.70   $64.70  
  Purchase #5 $113.27   10.280%   $124.9142   $124.91   $124.90   $124.90  
  Purchase #6 $60.64   4.866%   $63.5907   $63.59   $63.60   $63.60  
  Purchase #7 $214.89   11.736%   $240.1095   $240.11   $240.10   $240.10  
  7 purchase totals = $914.17       $987.5974   $987.59   $987.55   $987.60