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	$228.66	8.372%	$247.8034	$247.80	$247.80	$247.80
Purchase #2	$211.42	5.832%	$223.75	$223.75	$223.75	$223.80
Purchase #3	$68.63	4.370%	$71.6291	$71.63	$71.65	$71.60
Purchase #4	$28.25	12.430%	$31.7615	$31.76	$31.75	$31.80
Purchase #5	$69.92	11.598%	$78.0293	$78.03	$78.05	$78.00
Purchase #6	$158.68	12.221%	$178.0723	$178.07	$178.05	$178.10
Purchase #7	$79.31	4.356%	$82.7647	$82.76	$82.75	$82.80
7 purchase totals =	$844.87		$913.8103	$913.80	$913.80	$913.90