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 $204.59   4.388%   $213.5674   $213.57   $213.55   $213.60  
  Purchase #2 $250.27   10.164%   $275.7074   $275.71   $275.70   $275.70  
  Purchase #3 $102.28   5.321%   $107.7223   $107.72   $107.70   $107.70  
  Purchase #4 $147.87   3.420%   $152.9272   $152.93   $152.95   $152.90  
  Purchase #5 $162.79   11.439%   $181.4115   $181.41   $181.40   $181.40  
  Purchase #6 $157.30   4.732%   $164.7434   $164.74   $164.75   $164.70  
  Purchase #7 $153.97   11.173%   $171.1731   $171.17   $171.15   $171.20  
  7 purchase totals = $1,179.07       $1,267.2523   $1,267.25   $1,267.20   $1,267.20