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	$67.73	11.797%	$75.7201	$75.72	$75.70	$75.70
Purchase #2	$145.96	9.813%	$160.2831	$160.28	$160.30	$160.30
Purchase #3	$208.91	9.690%	$229.1534	$229.15	$229.15	$229.20
Purchase #4	$50.60	7.249%	$54.268	$54.27	$54.25	$54.30
Purchase #5	$192.78	9.502%	$211.098	$211.10	$211.10	$211.10
Purchase #6	$203.40	4.751%	$213.0635	$213.06	$213.05	$213.10
Purchase #7	$150.60	4.147%	$156.8454	$156.85	$156.85	$156.80
7 purchase totals =	$1,019.98		$1,100.4315	$1,100.43	$1,100.40	$1,100.50