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 $88.54   12.601%   $99.6969   $99.70   $99.70   $99.70  
  Purchase #2 $247.75   7.493%   $266.3139   $266.31   $266.30   $266.30  
  Purchase #3 $113.77   12.302%   $127.766   $127.77   $127.75   $127.80  
  Purchase #4 $60.26   5.320%   $63.4658   $63.47   $63.45   $63.50  
  Purchase #5 $107.90   8.679%   $117.2646   $117.26   $117.25   $117.30  
  Purchase #6 $61.43   5.203%   $64.6262   $64.63   $64.65   $64.60  
  Purchase #7 $45.72   7.548%   $49.1709   $49.17   $49.15   $49.20  
  7 purchase totals = $725.37       $788.3043   $788.31   $788.25   $788.40