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 $54.32   8.188%   $58.7677   $58.77   $58.75   $58.80  
  Purchase #2 $192.90   13.799%   $219.5183   $219.52   $219.50   $219.50  
  Purchase #3 $243.56   5.555%   $257.0898   $257.09   $257.10   $257.10  
  Purchase #4 $119.35   5.768%   $126.2341   $126.23   $126.25   $126.20  
  Purchase #5 $65.53   4.376%   $68.3976   $68.40   $68.40   $68.40  
  Purchase #6 $177.61   4.509%   $185.6184   $185.62   $185.60   $185.60  
  Purchase #7 $174.31   5.356%   $183.646   $183.65   $183.65   $183.60  
  7 purchase totals = $1,027.58       $1,099.2719   $1,099.28   $1,099.25   $1,099.20