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 $208.54   10.679%   $230.81   $230.81   $230.80   $230.80  
  Purchase #2 $246.28   12.708%   $277.5773   $277.58   $277.60   $277.60  
  Purchase #3 $126.83   10.702%   $140.4033   $140.40   $140.40   $140.40  
  Purchase #4 $241.26   7.125%   $258.4498   $258.45   $258.45   $258.40  
  Purchase #5 $54.62   5.406%   $57.5728   $57.57   $57.55   $57.60  
  Purchase #6 $136.96   11.161%   $152.2461   $152.25   $152.25   $152.20  
  Purchase #7 $169.97   4.482%   $177.5881   $177.59   $177.60   $177.60  
  7 purchase totals = $1,184.46       $1,294.6474   $1,294.65   $1,294.65   $1,294.60