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 $90.66   6.647%   $96.6862   $96.69   $96.70   $96.70  
  Purchase #2 $194.53   11.114%   $216.1501   $216.15   $216.15   $216.20  
  Purchase #3 $231.65   5.637%   $244.7081   $244.71   $244.70   $244.70  
  Purchase #4 $169.77   8.149%   $183.6046   $183.60   $183.60   $183.60  
  Purchase #5 $114.77   7.855%   $123.7852   $123.79   $123.80   $123.80  
  Purchase #6 $174.90   6.500%   $186.2685   $186.27   $186.25   $186.30  
  Purchase #7 $130.88   7.653%   $140.8962   $140.90   $140.90   $140.90  
  7 purchase totals = $1,107.16       $1,192.0989   $1,192.11   $1,192.10   $1,192.20