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	$104.67	5.539%	$110.4677	$110.47	$110.45	$110.50
Purchase #2	$248.32	6.563%	$264.6172	$264.62	$264.60	$264.60
Purchase #3	$67.63	13.106%	$76.4936	$76.49	$76.50	$76.50
Purchase #4	$120.33	6.134%	$127.711	$127.71	$127.70	$127.70
Purchase #5	$239.41	11.684%	$267.3827	$267.38	$267.40	$267.40
Purchase #6	$66.35	5.532%	$70.0205	$70.02	$70.00	$70.00
Purchase #7	$152.65	12.602%	$171.887	$171.89	$171.90	$171.90
7 purchase totals =	$999.36		$1,088.5797	$1,088.58	$1,088.55	$1,088.60