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	$167.59	3.463%	$173.3936	$173.39	$173.40	$173.40
Purchase #2	$46.73	8.105%	$50.5175	$50.52	$50.50	$50.50
Purchase #3	$79.28	12.764%	$89.3993	$89.40	$89.40	$89.40
Purchase #4	$148.89	13.432%	$168.8889	$168.89	$168.90	$168.90
Purchase #5	$206.81	10.559%	$228.6471	$228.65	$228.65	$228.60
Purchase #6	$187.70	9.120%	$204.8182	$204.82	$204.80	$204.80
Purchase #7	$175.83	10.368%	$194.0601	$194.06	$194.05	$194.10
7 purchase totals =	$1,012.83		$1,109.7247	$1,109.73	$1,109.70	$1,109.70