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	$23.41	7.588%	$25.1864	$25.19	$25.20	$25.20
Purchase #2	$103.96	4.685%	$108.8305	$108.83	$108.85	$108.80
Purchase #3	$174.97	7.268%	$187.6868	$187.69	$187.70	$187.70
Purchase #4	$210.49	6.200%	$223.5404	$223.54	$223.55	$223.50
Purchase #5	$241.41	11.660%	$269.5584	$269.56	$269.55	$269.60
Purchase #6	$156.81	5.474%	$165.3938	$165.39	$165.40	$165.40
Purchase #7	$101.49	9.612%	$111.2452	$111.25	$111.25	$111.20
7 purchase totals =	$1,012.54		$1,091.4415	$1,091.45	$1,091.50	$1,091.40