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	$40.38	13.370%	$45.7788	$45.78	$45.80	$45.80
Purchase #2	$160.86	4.284%	$167.7512	$167.75	$167.75	$167.80
Purchase #3	$114.61	9.559%	$125.5656	$125.57	$125.55	$125.60
Purchase #4	$80.70	10.810%	$89.4237	$89.42	$89.40	$89.40
Purchase #5	$52.92	3.714%	$54.8854	$54.89	$54.90	$54.90
Purchase #6	$92.51	7.749%	$99.6786	$99.68	$99.70	$99.70
Purchase #7	$158.73	5.853%	$168.0205	$168.02	$168.00	$168.00
7 purchase totals =	$700.71		$751.1038	$751.11	$751.10	$751.20