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	$127.39	13.385%	$144.4412	$144.44	$144.45	$144.40
Purchase #2	$219.66	11.562%	$245.0571	$245.06	$245.05	$245.10
Purchase #3	$82.56	7.833%	$89.0269	$89.03	$89.05	$89.00
Purchase #4	$146.72	3.730%	$152.1927	$152.19	$152.20	$152.20
Purchase #5	$43.76	12.677%	$49.3075	$49.31	$49.30	$49.30
Purchase #6	$107.87	7.675%	$116.149	$116.15	$116.15	$116.10
Purchase #7	$128.72	8.764%	$140.001	$140.00	$140.00	$140.00
7 purchase totals =	$856.68		$936.1754	$936.18	$936.20	$936.10