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 $152.79   7.196%   $163.7848   $163.78   $163.80   $163.80  
  Purchase #2 $61.46   8.809%   $66.874   $66.87   $66.85   $66.90  
  Purchase #3 $208.58   7.249%   $223.7   $223.70   $223.70   $223.70  
  Purchase #4 $92.62   4.127%   $96.4424   $96.44   $96.45   $96.40  
  Purchase #5 $248.96   8.194%   $269.3598   $269.36   $269.35   $269.40  
  Purchase #6 $62.48   3.171%   $64.4612   $64.46   $64.45   $64.50  
  Purchase #7 $108.52   5.744%   $114.7534   $114.75   $114.75   $114.80  
  7 purchase totals = $935.41       $999.3756   $999.36   $999.35   $999.50