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 $42.62   11.264%   $47.4207   $47.42   $47.40   $47.40  
  Purchase #2 $168.29   9.730%   $184.6646   $184.66   $184.65   $184.70  
  Purchase #3 $119.99   3.833%   $124.5892   $124.59   $124.60   $124.60  
  Purchase #4 $244.33   7.336%   $262.254   $262.25   $262.25   $262.30  
  Purchase #5 $193.75   6.707%   $206.7448   $206.74   $206.75   $206.70  
  Purchase #6 $84.81   3.184%   $87.5104   $87.51   $87.50   $87.50  
  Purchase #7 $160.37   8.853%   $174.5676   $174.57   $174.55   $174.60  
  7 purchase totals = $1,014.16       $1,087.7513   $1,087.74   $1,087.70   $1,087.80