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	$230.62	7.486%	$247.8842	$247.88	$247.90	$247.90
Purchase #2	$67.28	13.668%	$76.4758	$76.48	$76.50	$76.50
Purchase #3	$168.95	10.388%	$186.5005	$186.50	$186.50	$186.50
Purchase #4	$193.76	10.648%	$214.3916	$214.39	$214.40	$214.40
Purchase #5	$89.46	10.734%	$99.0626	$99.06	$99.05	$99.10
Purchase #6	$46.37	3.646%	$48.0607	$48.06	$48.05	$48.10
Purchase #7	$187.78	12.843%	$211.8966	$211.90	$211.90	$211.90
7 purchase totals =	$984.22		$1,084.2720	$1,084.27	$1,084.30	$1,084.40