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 $248.97   7.119%   $266.6942   $266.69   $266.70   $266.70  
  Purchase #2 $91.58   11.762%   $102.3516   $102.35   $102.35   $102.40  
  Purchase #3 $10.44   12.741%   $11.7702   $11.77   $11.75   $11.80  
  Purchase #4 $244.32   8.743%   $265.6809   $265.68   $265.70   $265.70  
  Purchase #5 $53.94   9.754%   $59.2013   $59.20   $59.20   $59.20  
  Purchase #6 $124.67   3.537%   $129.0796   $129.08   $129.10   $129.10  
  Purchase #7 $208.53   9.543%   $228.43   $228.43   $228.45   $228.40  
  7 purchase totals = $982.45       $1,063.2078   $1,063.20   $1,063.25   $1,063.30