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 $62.91   5.799%   $66.5582   $66.56   $66.55   $66.60  
  Purchase #2 $41.38   8.107%   $44.7347   $44.73   $44.75   $44.70  
  Purchase #3 $150.70   4.646%   $157.7015   $157.70   $157.70   $157.70  
  Purchase #4 $250.92   8.467%   $272.1654   $272.17   $272.15   $272.20  
  Purchase #5 $115.80   11.832%   $129.5015   $129.50   $129.50   $129.50  
  Purchase #6 $213.42   3.363%   $220.5973   $220.60   $220.60   $220.60  
  Purchase #7 $248.74   8.465%   $269.7958   $269.80   $269.80   $269.80  
  7 purchase totals = $1,083.87       $1,161.0544   $1,161.06   $1,161.05   $1,161.10