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	$83.77	5.234%	$88.1545	$88.15	$88.15	$88.20
Purchase #2	$102.39	11.506%	$114.171	$114.17	$114.15	$114.20
Purchase #3	$73.44	9.153%	$80.162	$80.16	$80.15	$80.20
Purchase #4	$54.81	11.772%	$61.2622	$61.26	$61.25	$61.30
Purchase #5	$116.98	8.556%	$126.9888	$126.99	$127.00	$127.00
Purchase #6	$183.89	6.766%	$196.332	$196.33	$196.35	$196.30
Purchase #7	$172.76	6.834%	$184.5664	$184.57	$184.55	$184.60
7 purchase totals =	$788.04		$851.6369	$851.63	$851.60	$851.80