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 $7.28   13.363%   $8.2528   $8.25   $8.25   $8.30  
  Purchase #2 $192.79   7.206%   $206.6824   $206.68   $206.70   $206.70  
  Purchase #3 $113.88   6.547%   $121.3357   $121.34   $121.35   $121.30  
  Purchase #4 $52.66   11.271%   $58.5953   $58.60   $58.60   $58.60  
  Purchase #5 $114.91   11.358%   $127.9615   $127.96   $127.95   $128.00  
  Purchase #6 $201.76   4.668%   $211.1782   $211.18   $211.20   $211.20  
  Purchase #7 $214.80   8.797%   $233.696   $233.70   $233.70   $233.70  
  7 purchase totals = $898.08       $967.7019   $967.71   $967.75   $967.80