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	$246.34	11.129%	$273.7552	$273.76	$273.75	$273.80
Purchase #2	$45.29	9.420%	$49.5563	$49.56	$49.55	$49.60
Purchase #3	$193.63	6.465%	$206.1482	$206.15	$206.15	$206.10
Purchase #4	$165.94	11.802%	$185.5242	$185.52	$185.50	$185.50
Purchase #5	$172.72	9.240%	$188.6793	$188.68	$188.70	$188.70
Purchase #6	$116.59	13.158%	$131.9309	$131.93	$131.95	$131.90
Purchase #7	$227.74	3.589%	$235.9136	$235.91	$235.90	$235.90
7 purchase totals =	$1,168.25		$1,271.5077	$1,271.51	$1,271.50	$1,271.50