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	$68.75	3.525%	$71.1734	$71.17	$71.15	$71.20
Purchase #2	$37.86	10.234%	$41.7346	$41.73	$41.75	$41.70
Purchase #3	$100.56	10.834%	$111.4547	$111.45	$111.45	$111.50
Purchase #4	$86.75	7.522%	$93.2753	$93.28	$93.30	$93.30
Purchase #5	$111.88	11.495%	$124.7406	$124.74	$124.75	$124.70
Purchase #6	$115.47	7.140%	$123.7146	$123.71	$123.70	$123.70
Purchase #7	$84.84	4.110%	$88.3269	$88.33	$88.35	$88.30
7 purchase totals =	$606.11		$654.4201	$654.41	$654.45	$654.40