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	$66.87	6.761%	$71.3911	$71.39	$71.40	$71.40
Purchase #2	$152.74	6.535%	$162.7216	$162.72	$162.70	$162.70
Purchase #3	$133.49	8.547%	$144.8994	$144.90	$144.90	$144.90
Purchase #4	$100.45	8.860%	$109.3499	$109.35	$109.35	$109.30
Purchase #5	$181.31	5.840%	$191.8985	$191.90	$191.90	$191.90
Purchase #6	$195.38	5.107%	$205.3581	$205.36	$205.35	$205.40
Purchase #7	$66.38	5.783%	$70.2188	$70.22	$70.20	$70.20
7 purchase totals =	$896.62		$955.8374	$955.84	$955.80	$955.80