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 $239.98   10.296%   $264.6883   $264.69   $264.70   $264.70  
  Purchase #2 $156.87   4.425%   $163.8115   $163.81   $163.80   $163.80  
  Purchase #3 $156.80   10.727%   $173.6199   $173.62   $173.60   $173.60  
  Purchase #4 $161.33   4.823%   $169.1109   $169.11   $169.10   $169.10  
  Purchase #5 $197.55   6.685%   $210.7562   $210.76   $210.75   $210.80  
  Purchase #6 $18.33   4.299%   $19.118   $19.12   $19.10   $19.10  
  Purchase #7 $114.29   10.602%   $126.407   $126.41   $126.40   $126.40  
  7 purchase totals = $1,045.15       $1,127.5118   $1,127.52   $1,127.45   $1,127.50