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 $53.82   4.786%   $56.3958   $56.40   $56.40   $56.40  
  Purchase #2 $114.85   8.159%   $124.2206   $124.22   $124.20   $124.20  
  Purchase #3 $104.31   4.785%   $109.3012   $109.30   $109.30   $109.30  
  Purchase #4 $234.97   6.269%   $249.7003   $249.70   $249.70   $249.70  
  Purchase #5 $206.51   4.373%   $215.5407   $215.54   $215.55   $215.50  
  Purchase #6 $221.72   4.853%   $232.4801   $232.48   $232.50   $232.50  
  Purchase #7 $175.57   7.742%   $189.1626   $189.16   $189.15   $189.20  
  7 purchase totals = $1,111.75       $1,176.8013   $1,176.80   $1,176.80   $1,176.80