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 $47.86   10.247%   $52.7642   $52.76   $52.75   $52.80  
  Purchase #2 $226.82   13.331%   $257.0574   $257.06   $257.05   $257.10  
  Purchase #3 $216.89   7.741%   $233.6795   $233.68   $233.70   $233.70  
  Purchase #4 $54.63   5.608%   $57.6937   $57.69   $57.70   $57.70  
  Purchase #5 $177.51   3.685%   $184.0512   $184.05   $184.05   $184.10  
  Purchase #6 $183.55   13.279%   $207.9236   $207.92   $207.90   $207.90  
  Purchase #7 $9.94   6.835%   $10.6194   $10.62   $10.60   $10.60  
  7 purchase totals = $917.20       $1,003.7890   $1,003.78   $1,003.75   $1,003.90