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	$106.56	12.713%	$120.107	$120.11	$120.10	$120.10
Purchase #2	$106.67	7.318%	$114.4761	$114.48	$114.50	$114.50
Purchase #3	$100.30	9.308%	$109.6359	$109.64	$109.65	$109.60
Purchase #4	$85.51	4.621%	$89.4614	$89.46	$89.45	$89.50
Purchase #5	$220.61	9.231%	$240.9745	$240.97	$240.95	$241.00
Purchase #6	$167.36	11.403%	$186.4441	$186.44	$186.45	$186.40
Purchase #7	$80.45	5.866%	$85.1692	$85.17	$85.15	$85.20
7 purchase totals =	$867.46		$946.2682	$946.27	$946.25	$946.30