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	$85.76	4.114%	$89.2882	$89.29	$89.30	$89.30
Purchase #2	$217.86	13.718%	$247.746	$247.75	$247.75	$247.70
Purchase #3	$185.84	13.432%	$210.802	$210.80	$210.80	$210.80
Purchase #4	$154.92	9.868%	$170.2075	$170.21	$170.20	$170.20
Purchase #5	$152.71	4.791%	$160.0263	$160.03	$160.05	$160.00
Purchase #6	$99.28	12.795%	$111.9829	$111.98	$112.00	$112.00
Purchase #7	$123.27	4.161%	$128.3993	$128.40	$128.40	$128.40
7 purchase totals =	$1,019.64		$1,118.4522	$1,118.46	$1,118.50	$1,118.40