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	$81.37	10.774%	$90.1368	$90.14	$90.15	$90.10
Purchase #2	$210.88	10.860%	$233.7816	$233.78	$233.80	$233.80
Purchase #3	$105.25	6.266%	$111.845	$111.85	$111.85	$111.80
Purchase #4	$40.51	12.654%	$45.6361	$45.64	$45.65	$45.60
Purchase #5	$223.31	7.163%	$239.3057	$239.31	$239.30	$239.30
Purchase #6	$170.63	7.200%	$182.9154	$182.92	$182.90	$182.90
Purchase #7	$142.26	12.285%	$159.7366	$159.74	$159.75	$159.70
7 purchase totals =	$974.21		$1,063.3572	$1,063.38	$1,063.40	$1,063.20