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	$19.97	9.645%	$21.8961	$21.90	$21.90	$21.90
Purchase #2	$161.31	9.328%	$176.357	$176.36	$176.35	$176.40
Purchase #3	$105.54	4.700%	$110.5004	$110.50	$110.50	$110.50
Purchase #4	$238.68	11.178%	$265.3597	$265.36	$265.35	$265.40
Purchase #5	$127.36	13.539%	$144.6033	$144.60	$144.60	$144.60
Purchase #6	$172.33	13.801%	$196.1133	$196.11	$196.10	$196.10
Purchase #7	$238.69	5.488%	$251.7893	$251.79	$251.80	$251.80
7 purchase totals =	$1,063.88		$1,166.6191	$1,166.62	$1,166.60	$1,166.70