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	$235.64	7.165%	$252.5236	$252.52	$252.50	$252.50
Purchase #2	$142.37	13.400%	$161.4476	$161.45	$161.45	$161.40
Purchase #3	$72.33	11.250%	$80.4671	$80.47	$80.45	$80.50
Purchase #4	$107.25	7.867%	$115.6874	$115.69	$115.70	$115.70
Purchase #5	$195.49	13.796%	$222.4598	$222.46	$222.45	$222.50
Purchase #6	$250.89	9.523%	$274.7823	$274.78	$274.80	$274.80
Purchase #7	$120.91	5.777%	$127.895	$127.90	$127.90	$127.90
7 purchase totals =	$1,124.88		$1,235.2628	$1,235.27	$1,235.25	$1,235.30