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	$30.61	6.676%	$32.6535	$32.65	$32.65	$32.70
Purchase #2	$29.81	6.292%	$31.6856	$31.69	$31.70	$31.70
Purchase #3	$154.25	7.503%	$165.8234	$165.82	$165.80	$165.80
Purchase #4	$105.72	7.231%	$113.3646	$113.36	$113.35	$113.40
Purchase #5	$155.99	10.263%	$171.9993	$172.00	$172.00	$172.00
Purchase #6	$233.43	12.732%	$263.1503	$263.15	$263.15	$263.20
Purchase #7	$218.64	11.666%	$244.1465	$244.15	$244.15	$244.10
7 purchase totals =	$928.45		$1,022.8232	$1,022.82	$1,022.80	$1,022.90