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 $91.96   4.777%   $96.3529   $96.35   $96.35   $96.40  
  Purchase #2 $135.83   7.319%   $145.7714   $145.77   $145.75   $145.80  
  Purchase #3 $166.99   12.529%   $187.9122   $187.91   $187.90   $187.90  
  Purchase #4 $47.45   10.428%   $52.3981   $52.40   $52.40   $52.40  
  Purchase #5 $248.41   8.465%   $269.4379   $269.44   $269.45   $269.40  
  Purchase #6 $230.55   12.709%   $259.8506   $259.85   $259.85   $259.90  
  Purchase #7 $30.37   6.726%   $32.4127   $32.41   $32.40   $32.40  
  7 purchase totals = $951.56       $1,044.1358   $1,044.13   $1,044.10   $1,044.20