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 $95.30   10.769%   $105.5629   $105.56   $105.55   $105.60  
  Purchase #2 $177.93   8.709%   $193.4259   $193.43   $193.45   $193.40  
  Purchase #3 $250.33   12.848%   $282.4924   $282.49   $282.50   $282.50  
  Purchase #4 $171.43   8.276%   $185.6175   $185.62   $185.60   $185.60  
  Purchase #5 $13.66   12.351%   $15.3471   $15.35   $15.35   $15.30  
  Purchase #6 $237.95   12.545%   $267.8008   $267.80   $267.80   $267.80  
  Purchase #7 $115.88   6.482%   $123.3913   $123.39   $123.40   $123.40  
  7 purchase totals = $1,062.48       $1,173.6379   $1,173.64   $1,173.65   $1,173.60