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 $141.29   11.607%   $157.6895   $157.69   $157.70   $157.70  
  Purchase #2 $233.27   6.470%   $248.3626   $248.36   $248.35   $248.40  
  Purchase #3 $151.63   7.668%   $163.257   $163.26   $163.25   $163.30  
  Purchase #4 $168.98   3.732%   $175.2863   $175.29   $175.30   $175.30  
  Purchase #5 $228.96   9.182%   $249.9831   $249.98   $250.00   $250.00  
  Purchase #6 $123.48   7.336%   $132.5385   $132.54   $132.55   $132.50  
  Purchase #7 $171.86   6.691%   $183.3592   $183.36   $183.35   $183.40  
  7 purchase totals = $1,219.47       $1,310.4762   $1,310.48   $1,310.50   $1,310.60