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	$67.51	11.737%	$75.4336	$75.43	$75.45	$75.40
Purchase #2	$180.49	12.336%	$202.7552	$202.76	$202.75	$202.80
Purchase #3	$75.92	3.690%	$78.7214	$78.72	$78.70	$78.70
Purchase #4	$98.71	7.143%	$105.7609	$105.76	$105.75	$105.80
Purchase #5	$74.39	4.260%	$77.559	$77.56	$77.55	$77.60
Purchase #6	$106.32	4.678%	$111.2936	$111.29	$111.30	$111.30
Purchase #7	$53.50	6.611%	$57.0369	$57.04	$57.05	$57.00
7 purchase totals =	$656.84		$708.5606	$708.56	$708.55	$708.60