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	$88.37	13.420%	$100.2293	$100.23	$100.25	$100.20
Purchase #2	$126.63	11.162%	$140.7644	$140.76	$140.75	$140.80
Purchase #3	$55.87	6.107%	$59.282	$59.28	$59.30	$59.30
Purchase #4	$237.26	11.226%	$263.8948	$263.89	$263.90	$263.90
Purchase #5	$74.89	13.765%	$85.1986	$85.20	$85.20	$85.20
Purchase #6	$38.68	12.581%	$43.5463	$43.55	$43.55	$43.50
Purchase #7	$219.93	10.115%	$242.1759	$242.18	$242.20	$242.20
7 purchase totals =	$841.63		$935.0913	$935.09	$935.15	$935.10