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	$178.51	3.533%	$184.8168	$184.82	$184.80	$184.80
Purchase #2	$54.82	8.516%	$59.4885	$59.49	$59.50	$59.50
Purchase #3	$236.39	3.461%	$244.5715	$244.57	$244.55	$244.60
Purchase #4	$84.41	7.727%	$90.9324	$90.93	$90.95	$90.90
Purchase #5	$62.94	7.764%	$67.8267	$67.83	$67.85	$67.80
Purchase #6	$73.55	7.561%	$79.1111	$79.11	$79.10	$79.10
Purchase #7	$161.64	10.590%	$178.7577	$178.76	$178.75	$178.80
7 purchase totals =	$852.26		$905.5047	$905.51	$905.50	$905.50