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 $49.93   13.457%   $56.6491   $56.65   $56.65   $56.60  
  Purchase #2 $29.82   3.255%   $30.7906   $30.79   $30.80   $30.80  
  Purchase #3 $187.56   10.153%   $206.603   $206.60   $206.60   $206.60  
  Purchase #4 $250.74   3.242%   $258.869   $258.87   $258.85   $258.90  
  Purchase #5 $238.43   3.717%   $247.2924   $247.29   $247.30   $247.30  
  Purchase #6 $183.48   13.192%   $207.6847   $207.68   $207.70   $207.70  
  Purchase #7 $38.95   9.188%   $42.5287   $42.53   $42.55   $42.50  
  7 purchase totals = $978.91       $1,050.4175   $1,050.41   $1,050.45   $1,050.40