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 $242.74   4.216%   $252.9739   $252.97   $252.95   $253.00  
  Purchase #2 $109.75   11.471%   $122.3394   $122.34   $122.35   $122.30  
  Purchase #3 $248.57   13.805%   $282.8851   $282.89   $282.90   $282.90  
  Purchase #4 $82.65   3.425%   $85.4808   $85.48   $85.50   $85.50  
  Purchase #5 $154.50   8.238%   $167.2277   $167.23   $167.25   $167.20  
  Purchase #6 $89.56   3.403%   $92.6077   $92.61   $92.60   $92.60  
  Purchase #7 $65.85   11.409%   $73.3628   $73.36   $73.35   $73.40  
  7 purchase totals = $993.62       $1,076.8774   $1,076.88   $1,076.90   $1,076.90