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	$12.92	5.109%	$13.5801	$13.58	$13.60	$13.60
Purchase #2	$55.54	6.571%	$59.1895	$59.19	$59.20	$59.20
Purchase #3	$54.71	5.817%	$57.8925	$57.89	$57.90	$57.90
Purchase #4	$136.90	5.585%	$144.5459	$144.55	$144.55	$144.50
Purchase #5	$42.40	6.417%	$45.1208	$45.12	$45.10	$45.10
Purchase #6	$149.73	3.313%	$154.6906	$154.69	$154.70	$154.70
Purchase #7	$151.64	6.532%	$161.5451	$161.55	$161.55	$161.50
7 purchase totals =	$603.84		$636.5645	$636.57	$636.60	$636.50