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	$77.95	3.560%	$80.725	$80.73	$80.75	$80.70
Purchase #2	$55.38	7.119%	$59.3225	$59.32	$59.30	$59.30
Purchase #3	$89.76	13.718%	$102.0733	$102.07	$102.05	$102.10
Purchase #4	$219.26	8.818%	$238.5943	$238.59	$238.60	$238.60
Purchase #5	$89.38	3.869%	$92.8381	$92.84	$92.85	$92.80
Purchase #6	$228.46	8.247%	$247.3011	$247.30	$247.30	$247.30
Purchase #7	$79.31	13.753%	$90.2175	$90.22	$90.20	$90.20
7 purchase totals =	$839.50		$911.0718	$911.07	$911.05	$911.00