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	$26.94	6.728%	$28.7525	$28.75	$28.75	$28.80
Purchase #2	$164.79	9.488%	$180.4253	$180.43	$180.45	$180.40
Purchase #3	$156.81	9.862%	$172.2746	$172.27	$172.25	$172.30
Purchase #4	$115.45	6.580%	$123.0466	$123.05	$123.05	$123.00
Purchase #5	$169.52	9.458%	$185.5532	$185.55	$185.55	$185.60
Purchase #6	$127.65	3.335%	$131.9071	$131.91	$131.90	$131.90
Purchase #7	$211.72	11.640%	$236.3642	$236.36	$236.35	$236.40
7 purchase totals =	$972.88		$1,058.3235	$1,058.32	$1,058.30	$1,058.40