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	$123.51	11.217%	$137.3641	$137.36	$137.35	$137.40
Purchase #2	$118.81	6.168%	$126.1382	$126.14	$126.15	$126.10
Purchase #3	$51.65	11.590%	$57.6362	$57.64	$57.65	$57.60
Purchase #4	$202.83	13.579%	$230.3723	$230.37	$230.35	$230.40
Purchase #5	$170.37	12.185%	$191.1296	$191.13	$191.15	$191.10
Purchase #6	$221.55	13.216%	$250.83	$250.83	$250.85	$250.80
Purchase #7	$82.56	10.647%	$91.3502	$91.35	$91.35	$91.40
7 purchase totals =	$971.28		$1,084.8206	$1,084.82	$1,084.85	$1,084.80