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	$165.69	13.146%	$187.4716	$187.47	$187.45	$187.50
Purchase #2	$50.63	11.478%	$56.4413	$56.44	$56.45	$56.40
Purchase #3	$226.79	3.786%	$235.3763	$235.38	$235.40	$235.40
Purchase #4	$53.49	13.215%	$60.5587	$60.56	$60.55	$60.60
Purchase #5	$137.90	5.422%	$145.3769	$145.38	$145.40	$145.40
Purchase #6	$184.51	3.709%	$191.3535	$191.35	$191.35	$191.40
Purchase #7	$207.75	6.308%	$220.8549	$220.85	$220.85	$220.90
7 purchase totals =	$1,026.76		$1,097.4332	$1,097.43	$1,097.45	$1,097.60