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	$38.28	12.126%	$42.9218	$42.92	$42.90	$42.90
Purchase #2	$232.35	11.796%	$259.758	$259.76	$259.75	$259.80
Purchase #3	$121.76	4.584%	$127.3415	$127.34	$127.35	$127.30
Purchase #4	$167.69	10.872%	$185.9213	$185.92	$185.90	$185.90
Purchase #5	$65.33	7.656%	$70.3317	$70.33	$70.35	$70.30
Purchase #6	$88.91	6.761%	$94.9212	$94.92	$94.90	$94.90
Purchase #7	$106.42	5.318%	$112.0794	$112.08	$112.10	$112.10
7 purchase totals =	$820.74		$893.2749	$893.27	$893.25	$893.20