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	$90.43	9.862%	$99.3482	$99.35	$99.35	$99.30
Purchase #2	$167.62	3.762%	$173.9259	$173.93	$173.95	$173.90
Purchase #3	$226.82	4.598%	$237.2492	$237.25	$237.25	$237.20
Purchase #4	$56.34	9.627%	$61.7639	$61.76	$61.75	$61.80
Purchase #5	$33.36	6.372%	$35.4857	$35.49	$35.50	$35.50
Purchase #6	$218.38	7.148%	$233.9898	$233.99	$234.00	$234.00
Purchase #7	$154.87	6.755%	$165.3315	$165.33	$165.35	$165.30
7 purchase totals =	$947.82		$1,007.0942	$1,007.10	$1,007.15	$1,007.00