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	$167.49	3.362%	$173.121	$173.12	$173.10	$173.10
Purchase #2	$116.99	5.332%	$123.2279	$123.23	$123.25	$123.20
Purchase #3	$37.56	4.166%	$39.1247	$39.12	$39.10	$39.10
Purchase #4	$157.86	13.122%	$178.5744	$178.57	$178.55	$178.60
Purchase #5	$235.36	8.376%	$255.0738	$255.07	$255.05	$255.10
Purchase #6	$248.96	6.240%	$264.4951	$264.50	$264.50	$264.50
Purchase #7	$24.67	12.639%	$27.788	$27.79	$27.80	$27.80
7 purchase totals =	$988.89		$1,061.4049	$1,061.40	$1,061.35	$1,061.40