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	$74.76	9.216%	$81.6499	$81.65	$81.65	$81.60
Purchase #2	$120.36	7.130%	$128.9417	$128.94	$128.95	$128.90
Purchase #3	$224.90	3.188%	$232.0698	$232.07	$232.05	$232.10
Purchase #4	$115.67	10.679%	$128.0224	$128.02	$128.00	$128.00
Purchase #5	$200.59	11.465%	$223.5876	$223.59	$223.60	$223.60
Purchase #6	$77.91	5.341%	$82.0712	$82.07	$82.05	$82.10
Purchase #7	$205.34	13.540%	$233.143	$233.14	$233.15	$233.10
7 purchase totals =	$1,019.53		$1,109.4856	$1,109.48	$1,109.45	$1,109.40