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 $232.88   13.495%   $264.3072   $264.31   $264.30   $264.30  
  Purchase #2 $203.85   5.304%   $214.6622   $214.66   $214.65   $214.70  
  Purchase #3 $58.51   6.422%   $62.2675   $62.27   $62.25   $62.30  
  Purchase #4 $154.45   5.268%   $162.5864   $162.59   $162.60   $162.60  
  Purchase #5 $245.90   5.452%   $259.3065   $259.31   $259.30   $259.30  
  Purchase #6 $38.58   3.569%   $39.9569   $39.96   $39.95   $40.00  
  Purchase #7 $25.80   3.116%   $26.6039   $26.60   $26.60   $26.60  
  7 purchase totals = $959.97       $1,029.6906   $1,029.70   $1,029.65   $1,029.80