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 $202.59   8.225%   $219.253   $219.25   $219.25   $219.30  
  Purchase #2 $35.30   9.537%   $38.6666   $38.67   $38.65   $38.70  
  Purchase #3 $205.99   4.103%   $214.4418   $214.44   $214.45   $214.40  
  Purchase #4 $61.47   7.671%   $66.1854   $66.19   $66.20   $66.20  
  Purchase #5 $31.77   8.231%   $34.385   $34.39   $34.40   $34.40  
  Purchase #6 $24.84   4.599%   $25.9824   $25.98   $26.00   $26.00  
  Purchase #7 $226.49   9.386%   $247.7484   $247.75   $247.75   $247.70  
  7 purchase totals = $788.45       $846.6626   $846.67   $846.70   $846.70