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	$81.28	10.550%	$89.855	$89.86	$89.85	$89.90
Purchase #2	$146.61	3.739%	$152.0917	$152.09	$152.10	$152.10
Purchase #3	$41.91	9.288%	$45.8026	$45.80	$45.80	$45.80
Purchase #4	$70.30	3.251%	$72.5855	$72.59	$72.60	$72.60
Purchase #5	$246.53	7.285%	$264.4897	$264.49	$264.50	$264.50
Purchase #6	$100.70	10.521%	$111.2946	$111.29	$111.30	$111.30
Purchase #7	$171.71	9.831%	$188.5908	$188.59	$188.60	$188.60
7 purchase totals =	$859.04		$924.7099	$924.71	$924.75	$924.80