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	$50.62	12.554%	$56.9748	$56.97	$56.95	$57.00
Purchase #2	$159.89	9.585%	$175.2155	$175.22	$175.20	$175.20
Purchase #3	$39.30	3.197%	$40.5564	$40.56	$40.55	$40.60
Purchase #4	$112.77	13.662%	$128.1766	$128.18	$128.20	$128.20
Purchase #5	$94.47	4.813%	$99.0168	$99.02	$99.00	$99.00
Purchase #6	$89.96	11.766%	$100.5447	$100.54	$100.55	$100.50
Purchase #7	$211.44	8.214%	$228.8077	$228.81	$228.80	$228.80
7 purchase totals =	$758.45		$829.2925	$829.30	$829.25	$829.30