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	$142.76	10.738%	$158.0896	$158.09	$158.10	$158.10
Purchase #2	$178.29	13.477%	$202.3181	$202.32	$202.30	$202.30
Purchase #3	$119.39	6.631%	$127.3068	$127.31	$127.30	$127.30
Purchase #4	$154.92	10.421%	$171.0642	$171.06	$171.05	$171.10
Purchase #5	$170.72	11.244%	$189.9158	$189.92	$189.90	$189.90
Purchase #6	$248.80	13.126%	$281.4575	$281.46	$281.45	$281.50
Purchase #7	$41.25	4.656%	$43.1706	$43.17	$43.15	$43.20
7 purchase totals =	$1,056.13		$1,173.3226	$1,173.33	$1,173.25	$1,173.40