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 $111.48   5.382%   $117.4799   $117.48   $117.50   $117.50  
  Purchase #2 $203.49   6.233%   $216.1735   $216.17   $216.15   $216.20  
  Purchase #3 $141.49   11.453%   $157.6948   $157.69   $157.70   $157.70  
  Purchase #4 $216.92   11.344%   $241.5274   $241.53   $241.55   $241.50  
  Purchase #5 $164.45   4.787%   $172.3222   $172.32   $172.30   $172.30  
  Purchase #6 $211.29   9.835%   $232.0704   $232.07   $232.05   $232.10  
  Purchase #7 $114.25   6.747%   $121.9584   $121.96   $121.95   $122.00  
  7 purchase totals = $1,163.37       $1,259.2266   $1,259.22   $1,259.20   $1,259.30