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 $245.71   4.559%   $256.9119   $256.91   $256.90   $256.90  
  Purchase #2 $30.97   11.568%   $34.5526   $34.55   $34.55   $34.60  
  Purchase #3 $121.67   9.603%   $133.354   $133.35   $133.35   $133.40  
  Purchase #4 $153.49   10.815%   $170.0899   $170.09   $170.10   $170.10  
  Purchase #5 $187.48   8.155%   $202.769   $202.77   $202.75   $202.80  
  Purchase #6 $39.96   13.135%   $45.2087   $45.21   $45.20   $45.20  
  Purchase #7 $183.94   3.737%   $190.8138   $190.81   $190.80   $190.80  
  7 purchase totals = $963.22       $1,033.6999   $1,033.69   $1,033.65   $1,033.80