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	$92.27	4.306%	$96.2431	$96.24	$96.25	$96.20
Purchase #2	$222.77	7.753%	$240.0414	$240.04	$240.05	$240.00
Purchase #3	$90.39	10.578%	$99.9515	$99.95	$99.95	$100.00
Purchase #4	$224.84	3.557%	$232.8376	$232.84	$232.85	$232.80
Purchase #5	$155.57	10.654%	$172.1444	$172.14	$172.15	$172.10
Purchase #6	$137.25	12.679%	$154.6519	$154.65	$154.65	$154.70
Purchase #7	$73.80	11.541%	$82.3173	$82.32	$82.30	$82.30
7 purchase totals =	$996.89		$1,078.1872	$1,078.18	$1,078.20	$1,078.10