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	$169.71	5.407%	$178.8862	$178.89	$178.90	$178.90
Purchase #2	$205.71	8.425%	$223.0411	$223.04	$223.05	$223.00
Purchase #3	$67.48	6.861%	$72.1098	$72.11	$72.10	$72.10
Purchase #4	$17.32	5.555%	$18.2821	$18.28	$18.30	$18.30
Purchase #5	$52.35	4.228%	$54.5634	$54.56	$54.55	$54.60
Purchase #6	$240.43	13.305%	$272.4192	$272.42	$272.40	$272.40
Purchase #7	$81.83	9.172%	$89.3354	$89.34	$89.35	$89.30
7 purchase totals =	$834.83		$908.6372	$908.64	$908.65	$908.60