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 $59.94   6.852%   $64.0471   $64.05   $64.05   $64.00  
  Purchase #2 $167.62   9.416%   $183.4031   $183.40   $183.40   $183.40  
  Purchase #3 $81.51   10.481%   $90.0531   $90.05   $90.05   $90.10  
  Purchase #4 $207.77   12.467%   $233.6727   $233.67   $233.65   $233.70  
  Purchase #5 $20.95   9.552%   $22.9511   $22.95   $22.95   $23.00  
  Purchase #6 $148.41   3.157%   $153.0953   $153.10   $153.10   $153.10  
  Purchase #7 $191.80   13.593%   $217.8714   $217.87   $217.85   $217.90  
  7 purchase totals = $878.00       $965.0938   $965.09   $965.05   $965.20