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 $84.47   9.569%   $92.5529   $92.55   $92.55   $92.60  
  Purchase #2 $139.69   3.590%   $144.7049   $144.70   $144.70   $144.70  
  Purchase #3 $45.73   9.159%   $49.9184   $49.92   $49.90   $49.90  
  Purchase #4 $161.69   3.609%   $167.5254   $167.53   $167.55   $167.50  
  Purchase #5 $231.42   4.690%   $242.2736   $242.27   $242.25   $242.30  
  Purchase #6 $26.63   9.115%   $29.0573   $29.06   $29.05   $29.10  
  Purchase #7 $63.29   13.400%   $71.7709   $71.77   $71.75   $71.80  
  7 purchase totals = $752.92       $797.8034   $797.80   $797.75   $797.90