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 $42.42   6.655%   $45.2431   $45.24   $45.25   $45.20  
  Purchase #2 $219.54   9.154%   $239.6367   $239.64   $239.65   $239.60  
  Purchase #3 $87.77   4.689%   $91.8855   $91.89   $91.90   $91.90  
  Purchase #4 $237.40   4.756%   $248.6907   $248.69   $248.70   $248.70  
  Purchase #5 $158.43   11.275%   $176.293   $176.29   $176.30   $176.30  
  Purchase #6 $99.53   8.451%   $107.9413   $107.94   $107.95   $107.90  
  Purchase #7 $230.70   12.555%   $259.6644   $259.66   $259.65   $259.70  
  7 purchase totals = $1,075.79       $1,169.3547   $1,169.35   $1,169.40   $1,169.30