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 $108.64   9.149%   $118.5795   $118.58   $118.60   $118.60  
  Purchase #2 $127.47   10.132%   $140.3853   $140.39   $140.40   $140.40  
  Purchase #3 $19.29   3.443%   $19.9542   $19.95   $19.95   $20.00  
  Purchase #4 $216.83   10.643%   $239.9072   $239.91   $239.90   $239.90  
  Purchase #5 $183.64   9.107%   $200.3641   $200.36   $200.35   $200.40  
  Purchase #6 $87.51   8.577%   $95.0157   $95.02   $95.00   $95.00  
  Purchase #7 $43.59   9.766%   $47.847   $47.85   $47.85   $47.80  
  7 purchase totals = $786.97       $862.0530   $862.06   $862.05   $862.10