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	$37.70	6.357%	$40.0966	$40.10	$40.10	$40.10
Purchase #2	$247.78	6.460%	$263.7866	$263.79	$263.80	$263.80
Purchase #3	$240.85	9.429%	$263.5597	$263.56	$263.55	$263.60
Purchase #4	$127.35	9.849%	$139.8927	$139.89	$139.90	$139.90
Purchase #5	$126.56	12.376%	$142.2231	$142.22	$142.20	$142.20
Purchase #6	$87.59	5.498%	$92.4057	$92.41	$92.40	$92.40
Purchase #7	$216.57	12.563%	$243.7777	$243.78	$243.80	$243.80
7 purchase totals =	$1,084.40		$1,185.7421	$1,185.75	$1,185.75	$1,185.80