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	$204.28	6.156%	$216.8555	$216.86	$216.85	$216.90
Purchase #2	$93.33	6.723%	$99.6046	$99.60	$99.60	$99.60
Purchase #3	$42.72	7.380%	$45.8727	$45.87	$45.85	$45.90
Purchase #4	$80.69	11.312%	$89.8177	$89.82	$89.80	$89.80
Purchase #5	$28.74	8.586%	$31.2076	$31.21	$31.20	$31.20
Purchase #6	$231.47	9.802%	$254.1587	$254.16	$254.15	$254.20
Purchase #7	$62.73	4.108%	$65.3069	$65.31	$65.30	$65.30
7 purchase totals =	$743.96		$802.8237	$802.83	$802.75	$802.90