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	$172.29	3.417%	$178.1771	$178.18	$178.20	$178.20
Purchase #2	$186.36	7.412%	$200.173	$200.17	$200.15	$200.20
Purchase #3	$20.57	7.711%	$22.1562	$22.16	$22.15	$22.20
Purchase #4	$160.67	11.526%	$179.1888	$179.19	$179.20	$179.20
Purchase #5	$138.92	9.303%	$151.8437	$151.84	$151.85	$151.80
Purchase #6	$148.28	3.764%	$153.8613	$153.86	$153.85	$153.90
Purchase #7	$199.86	12.288%	$224.4188	$224.42	$224.40	$224.40
7 purchase totals =	$1,026.95		$1,109.8189	$1,109.82	$1,109.80	$1,109.90