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	$80.99	10.506%	$89.4988	$89.50	$89.50	$89.50
Purchase #2	$31.36	7.692%	$33.7722	$33.77	$33.75	$33.80
Purchase #3	$52.40	4.632%	$54.8272	$54.83	$54.85	$54.80
Purchase #4	$28.32	10.429%	$31.2735	$31.27	$31.25	$31.30
Purchase #5	$158.47	10.435%	$175.0063	$175.01	$175.00	$175.00
Purchase #6	$188.95	4.114%	$196.7234	$196.72	$196.70	$196.70
Purchase #7	$68.70	11.740%	$76.7654	$76.77	$76.75	$76.80
7 purchase totals =	$609.19		$657.8668	$657.87	$657.80	$657.90