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 $114.67   4.421%   $119.7396   $119.74   $119.75   $119.70  
  Purchase #2 $41.85   11.409%   $46.6247   $46.62   $46.60   $46.60  
  Purchase #3 $69.94   5.679%   $73.9119   $73.91   $73.90   $73.90  
  Purchase #4 $205.60   13.196%   $232.731   $232.73   $232.75   $232.70  
  Purchase #5 $173.62   7.470%   $186.5894   $186.59   $186.60   $186.60  
  Purchase #6 $54.31   3.425%   $56.1701   $56.17   $56.15   $56.20  
  Purchase #7 $221.68   11.215%   $246.5414   $246.54   $246.55   $246.50  
  7 purchase totals = $881.67       $962.3081   $962.30   $962.30   $962.20