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	$148.31	11.538%	$165.422	$165.42	$165.40	$165.40
Purchase #2	$19.29	12.609%	$21.7223	$21.72	$21.70	$21.70
Purchase #3	$92.70	12.567%	$104.3496	$104.35	$104.35	$104.30
Purchase #4	$128.45	5.229%	$135.1667	$135.17	$135.15	$135.20
Purchase #5	$58.26	6.637%	$62.1267	$62.13	$62.15	$62.10
Purchase #6	$129.72	7.862%	$139.9186	$139.92	$139.90	$139.90
Purchase #7	$66.69	7.693%	$71.8205	$71.82	$71.80	$71.80
7 purchase totals =	$643.42		$700.5264	$700.53	$700.45	$700.40