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	$74.42	12.164%	$83.4724	$83.47	$83.45	$83.50
Purchase #2	$130.32	11.140%	$144.8376	$144.84	$144.85	$144.80
Purchase #3	$37.57	12.304%	$42.1926	$42.19	$42.20	$42.20
Purchase #4	$181.71	8.424%	$197.0173	$197.02	$197.00	$197.00
Purchase #5	$59.45	4.815%	$62.3125	$62.31	$62.30	$62.30
Purchase #6	$72.72	6.156%	$77.1966	$77.20	$77.20	$77.20
Purchase #7	$83.29	9.617%	$91.3	$91.30	$91.30	$91.30
7 purchase totals =	$639.48		$698.3290	$698.33	$698.30	$698.30