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	$136.34	12.149%	$152.9039	$152.90	$152.90	$152.90
Purchase #2	$117.94	11.422%	$131.4111	$131.41	$131.40	$131.40
Purchase #3	$59.63	10.335%	$65.7928	$65.79	$65.80	$65.80
Purchase #4	$48.33	10.498%	$53.4037	$53.40	$53.40	$53.40
Purchase #5	$223.56	6.512%	$238.1182	$238.12	$238.10	$238.10
Purchase #6	$45.38	12.163%	$50.8996	$50.90	$50.90	$50.90
Purchase #7	$13.46	5.619%	$14.2163	$14.22	$14.20	$14.20
7 purchase totals =	$644.64		$706.7456	$706.74	$706.70	$706.70