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 $41.53   5.482%   $43.8067   $43.81   $43.80   $43.80  
  Purchase #2 $164.56   5.571%   $173.7276   $173.73   $173.75   $173.70  
  Purchase #3 $114.94   10.414%   $126.9099   $126.91   $126.90   $126.90  
  Purchase #4 $114.28   5.564%   $120.6385   $120.64   $120.65   $120.60  
  Purchase #5 $169.57   5.235%   $178.447   $178.45   $178.45   $178.40  
  Purchase #6 $81.74   4.496%   $85.415   $85.42   $85.40   $85.40  
  Purchase #7 $109.68   4.695%   $114.8295   $114.83   $114.85   $114.80  
  7 purchase totals = $796.30       $843.7742   $843.79   $843.80   $843.60