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	$120.72	11.333%	$134.4012	$134.40	$134.40	$134.40
Purchase #2	$178.88	3.822%	$185.7168	$185.72	$185.70	$185.70
Purchase #3	$31.84	7.865%	$34.3442	$34.34	$34.35	$34.30
Purchase #4	$53.45	13.219%	$60.5156	$60.52	$60.50	$60.50
Purchase #5	$63.94	11.500%	$71.2931	$71.29	$71.30	$71.30
Purchase #6	$243.46	9.867%	$267.4822	$267.48	$267.50	$267.50
Purchase #7	$128.32	13.316%	$145.4071	$145.41	$145.40	$145.40
7 purchase totals =	$820.61		$899.1602	$899.16	$899.15	$899.10