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 $210.35   7.729%   $226.608   $226.61   $226.60   $226.60  
  Purchase #2 $105.81   13.663%   $120.2668   $120.27   $120.25   $120.30  
  Purchase #3 $248.48   5.721%   $262.6955   $262.70   $262.70   $262.70  
  Purchase #4 $49.62   8.351%   $53.7638   $53.76   $53.75   $53.80  
  Purchase #5 $124.48   10.835%   $137.9674   $137.97   $137.95   $138.00  
  Purchase #6 $187.58   6.830%   $200.3917   $200.39   $200.40   $200.40  
  Purchase #7 $54.34   10.830%   $60.225   $60.23   $60.25   $60.20  
  7 purchase totals = $980.66       $1,061.9182   $1,061.93   $1,061.90   $1,062.00