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 $152.41   8.572%   $165.4746   $165.47   $165.45   $165.50  
  Purchase #2 $168.63   11.215%   $187.5419   $187.54   $187.55   $187.50  
  Purchase #3 $227.72   12.675%   $256.5835   $256.58   $256.60   $256.60  
  Purchase #4 $15.99   5.727%   $16.9057   $16.91   $16.90   $16.90  
  Purchase #5 $157.90   5.409%   $166.4408   $166.44   $166.45   $166.40  
  Purchase #6 $101.45   11.374%   $112.9889   $112.99   $113.00   $113.00  
  Purchase #7 $144.55   5.824%   $152.9686   $152.97   $152.95   $153.00  
  7 purchase totals = $968.65       $1,058.9040   $1,058.90   $1,058.90   $1,058.90