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	$108.62	10.524%	$120.0512	$120.05	$120.05	$120.10
Purchase #2	$159.41	10.355%	$175.9169	$175.92	$175.90	$175.90
Purchase #3	$225.89	8.556%	$245.2171	$245.22	$245.20	$245.20
Purchase #4	$200.93	10.585%	$222.1984	$222.20	$222.20	$222.20
Purchase #5	$92.65	8.313%	$100.352	$100.35	$100.35	$100.40
Purchase #6	$239.79	13.408%	$271.941	$271.94	$271.95	$271.90
Purchase #7	$32.35	10.738%	$35.8237	$35.82	$35.80	$35.80
7 purchase totals =	$1,059.64		$1,171.5003	$1,171.50	$1,171.45	$1,171.50