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	$104.34	5.170%	$109.7344	$109.73	$109.75	$109.70
Purchase #2	$78.80	12.194%	$88.4089	$88.41	$88.40	$88.40
Purchase #3	$132.77	3.254%	$137.0903	$137.09	$137.10	$137.10
Purchase #4	$52.66	13.710%	$59.8797	$59.88	$59.90	$59.90
Purchase #5	$90.76	12.821%	$102.3963	$102.40	$102.40	$102.40
Purchase #6	$67.99	10.161%	$74.8985	$74.90	$74.90	$74.90
Purchase #7	$159.49	5.486%	$168.2396	$168.24	$168.25	$168.20
7 purchase totals =	$686.81		$740.6477	$740.65	$740.70	$740.60