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 $66.44   8.813%   $72.2954   $72.30   $72.30   $72.30  
  Purchase #2 $50.56   5.458%   $53.3196   $53.32   $53.30   $53.30  
  Purchase #3 $67.56   4.526%   $70.6178   $70.62   $70.60   $70.60  
  Purchase #4 $154.95   4.675%   $162.1939   $162.19   $162.20   $162.20  
  Purchase #5 $174.29   8.856%   $189.7251   $189.73   $189.75   $189.70  
  Purchase #6 $187.28   5.861%   $198.2565   $198.26   $198.25   $198.30  
  Purchase #7 $58.33   3.107%   $60.1423   $60.14   $60.15   $60.10  
  7 purchase totals = $759.41       $806.5506   $806.56   $806.55   $806.50