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	$205.91	10.841%	$228.2327	$228.23	$228.25	$228.20
Purchase #2	$98.88	10.647%	$109.4078	$109.41	$109.40	$109.40
Purchase #3	$171.67	11.294%	$191.0584	$191.06	$191.05	$191.10
Purchase #4	$129.90	9.790%	$142.6172	$142.62	$142.60	$142.60
Purchase #5	$151.27	5.152%	$159.0634	$159.06	$159.05	$159.10
Purchase #6	$83.47	12.629%	$94.0114	$94.01	$94.00	$94.00
Purchase #7	$193.80	13.198%	$219.3777	$219.38	$219.40	$219.40
7 purchase totals =	$1,034.90		$1,143.7686	$1,143.77	$1,143.75	$1,143.80