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	$52.74	12.407%	$59.2835	$59.28	$59.30	$59.30
Purchase #2	$172.29	9.611%	$188.8488	$188.85	$188.85	$188.80
Purchase #3	$180.92	10.149%	$199.2816	$199.28	$199.30	$199.30
Purchase #4	$176.91	11.199%	$196.7222	$196.72	$196.70	$196.70
Purchase #5	$123.99	3.155%	$127.9019	$127.90	$127.90	$127.90
Purchase #6	$82.83	12.537%	$93.2144	$93.21	$93.20	$93.20
Purchase #7	$57.68	3.501%	$59.6994	$59.70	$59.70	$59.70
7 purchase totals =	$847.36		$924.9518	$924.94	$924.95	$924.90