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	$246.56	9.598%	$270.2248	$270.22	$270.20	$270.20
Purchase #2	$57.43	4.538%	$60.0362	$60.04	$60.05	$60.00
Purchase #3	$42.88	12.591%	$48.279	$48.28	$48.30	$48.30
Purchase #4	$84.62	6.445%	$90.0738	$90.07	$90.05	$90.10
Purchase #5	$92.95	8.631%	$100.9725	$100.97	$100.95	$101.00
Purchase #6	$19.54	6.596%	$20.8289	$20.83	$20.85	$20.80
Purchase #7	$25.97	4.372%	$27.1054	$27.11	$27.10	$27.10
7 purchase totals =	$569.95		$617.5206	$617.52	$617.50	$617.50