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 $214.28   8.656%   $232.8281   $232.83   $232.85   $232.80  
  Purchase #2 $80.48   11.174%   $89.4728   $89.47   $89.45   $89.50  
  Purchase #3 $79.51   8.824%   $86.526   $86.53   $86.55   $86.50  
  Purchase #4 $91.62   8.870%   $99.7467   $99.75   $99.75   $99.70  
  Purchase #5 $183.30   5.649%   $193.6546   $193.65   $193.65   $193.70  
  Purchase #6 $242.54   3.743%   $251.6183   $251.62   $251.60   $251.60  
  Purchase #7 $70.38   7.831%   $75.8915   $75.89   $75.90   $75.90  
  7 purchase totals = $962.11       $1,029.7380   $1,029.74   $1,029.75   $1,029.70