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	$94.41	5.728%	$99.8178	$99.82	$99.80	$99.80
Purchase #2	$169.97	7.118%	$182.0685	$182.07	$182.05	$182.10
Purchase #3	$59.51	5.274%	$62.6486	$62.65	$62.65	$62.60
Purchase #4	$81.31	10.773%	$90.0695	$90.07	$90.05	$90.10
Purchase #5	$23.33	5.361%	$24.5807	$24.58	$24.60	$24.60
Purchase #6	$10.26	3.320%	$10.6006	$10.60	$10.60	$10.60
Purchase #7	$73.78	9.661%	$80.9079	$80.91	$80.90	$80.90
7 purchase totals =	$512.57		$550.6936	$550.70	$550.65	$550.70