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	$80.25	11.311%	$89.3271	$89.33	$89.35	$89.30
Purchase #2	$222.99	3.585%	$230.9842	$230.98	$231.00	$231.00
Purchase #3	$171.39	10.412%	$189.2351	$189.24	$189.25	$189.20
Purchase #4	$18.25	11.525%	$20.3533	$20.35	$20.35	$20.40
Purchase #5	$229.97	5.353%	$242.2803	$242.28	$242.30	$242.30
Purchase #6	$95.92	4.111%	$99.8633	$99.86	$99.85	$99.90
Purchase #7	$109.69	9.500%	$120.1106	$120.11	$120.10	$120.10
7 purchase totals =	$928.46		$992.1539	$992.15	$992.20	$992.20