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	$72.60	7.490%	$78.0377	$78.04	$78.05	$78.00
Purchase #2	$45.71	6.664%	$48.7561	$48.76	$48.75	$48.80
Purchase #3	$75.28	13.640%	$85.5482	$85.55	$85.55	$85.50
Purchase #4	$99.29	13.285%	$112.4807	$112.48	$112.50	$112.50
Purchase #5	$101.39	9.228%	$110.7463	$110.75	$110.75	$110.70
Purchase #6	$79.70	5.746%	$84.2796	$84.28	$84.30	$84.30
Purchase #7	$63.40	5.718%	$67.0252	$67.03	$67.05	$67.00
7 purchase totals =	$537.37		$586.8738	$586.89	$586.95	$586.80