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	$51.68	7.233%	$55.418	$55.42	$55.40	$55.40
Purchase #2	$223.94	6.335%	$238.1266	$238.13	$238.15	$238.10
Purchase #3	$173.31	4.278%	$180.7242	$180.72	$180.70	$180.70
Purchase #4	$137.34	12.373%	$154.3331	$154.33	$154.35	$154.30
Purchase #5	$69.89	4.399%	$72.9645	$72.96	$72.95	$73.00
Purchase #6	$246.86	11.872%	$276.1672	$276.17	$276.15	$276.20
Purchase #7	$136.65	6.527%	$145.5691	$145.57	$145.55	$145.60
7 purchase totals =	$1,039.67		$1,123.3027	$1,123.30	$1,123.25	$1,123.30