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	$249.40	9.597%	$273.3349	$273.33	$273.35	$273.30
Purchase #2	$34.78	13.223%	$39.379	$39.38	$39.40	$39.40
Purchase #3	$72.72	7.530%	$78.1958	$78.20	$78.20	$78.20
Purchase #4	$153.57	13.472%	$174.259	$174.26	$174.25	$174.30
Purchase #5	$227.56	11.482%	$253.6884	$253.69	$253.70	$253.70
Purchase #6	$56.82	12.164%	$63.7316	$63.73	$63.75	$63.70
Purchase #7	$244.55	11.532%	$272.7515	$272.75	$272.75	$272.80
7 purchase totals =	$1,039.40		$1,155.3402	$1,155.34	$1,155.40	$1,155.40