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 $250.54   4.215%   $261.1003   $261.10   $261.10   $261.10  
  Purchase #2 $164.83   12.191%   $184.9244   $184.92   $184.90   $184.90  
  Purchase #3 $5.94   6.339%   $6.3165   $6.32   $6.30   $6.30  
  Purchase #4 $207.84   9.592%   $227.776   $227.78   $227.80   $227.80  
  Purchase #5 $109.62   5.488%   $115.6359   $115.64   $115.65   $115.60  
  Purchase #6 $127.54   4.362%   $133.1033   $133.10   $133.10   $133.10  
  Purchase #7 $216.80   13.654%   $246.4019   $246.40   $246.40   $246.40  
  7 purchase totals = $1,083.11       $1,175.2583   $1,175.26   $1,175.25   $1,175.20