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	$133.41	11.828%	$149.1897	$149.19	$149.20	$149.20
Purchase #2	$201.45	11.449%	$224.514	$224.51	$224.50	$224.50
Purchase #3	$25.27	10.675%	$27.9676	$27.97	$27.95	$28.00
Purchase #4	$132.44	9.123%	$144.5225	$144.52	$144.50	$144.50
Purchase #5	$188.75	4.141%	$196.5661	$196.57	$196.55	$196.60
Purchase #6	$98.55	4.830%	$103.31	$103.31	$103.30	$103.30
Purchase #7	$38.42	10.171%	$42.3277	$42.33	$42.35	$42.30
7 purchase totals =	$818.29		$888.3976	$888.40	$888.35	$888.40