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	$208.42	7.677%	$224.4204	$224.42	$224.40	$224.40
Purchase #2	$137.92	9.400%	$150.8845	$150.88	$150.90	$150.90
Purchase #3	$130.85	12.663%	$147.4195	$147.42	$147.40	$147.40
Purchase #4	$89.82	3.415%	$92.8874	$92.89	$92.90	$92.90
Purchase #5	$210.89	8.840%	$229.5327	$229.53	$229.55	$229.50
Purchase #6	$166.79	13.309%	$188.9881	$188.99	$189.00	$189.00
Purchase #7	$35.71	6.714%	$38.1076	$38.11	$38.10	$38.10
7 purchase totals =	$980.40		$1,072.2402	$1,072.24	$1,072.25	$1,072.20