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	$166.93	10.474%	$184.4142	$184.41	$184.40	$184.40
Purchase #2	$143.77	4.546%	$150.3058	$150.31	$150.30	$150.30
Purchase #3	$57.62	6.411%	$61.314	$61.31	$61.30	$61.30
Purchase #4	$146.32	12.690%	$164.888	$164.89	$164.90	$164.90
Purchase #5	$94.27	11.179%	$104.8084	$104.81	$104.80	$104.80
Purchase #6	$35.62	12.462%	$40.059	$40.06	$40.05	$40.10
Purchase #7	$145.48	3.796%	$151.0024	$151.00	$151.00	$151.00
7 purchase totals =	$790.01		$856.7918	$856.79	$856.75	$856.80