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	$157.75	9.286%	$172.3987	$172.40	$172.40	$172.40
Purchase #2	$162.57	7.472%	$174.7172	$174.72	$174.70	$174.70
Purchase #3	$145.69	13.581%	$165.4762	$165.48	$165.50	$165.50
Purchase #4	$104.71	7.590%	$112.6575	$112.66	$112.65	$112.70
Purchase #5	$196.78	11.537%	$219.4825	$219.48	$219.50	$219.50
Purchase #6	$39.94	6.786%	$42.6503	$42.65	$42.65	$42.70
Purchase #7	$238.77	5.352%	$251.549	$251.55	$251.55	$251.50
7 purchase totals =	$1,046.21		$1,138.9314	$1,138.94	$1,138.95	$1,139.00