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	$234.77	11.329%	$261.3671	$261.37	$261.35	$261.40
Purchase #2	$171.29	6.199%	$181.9083	$181.91	$181.90	$181.90
Purchase #3	$135.69	6.211%	$144.1177	$144.12	$144.10	$144.10
Purchase #4	$40.91	10.359%	$45.1479	$45.15	$45.15	$45.10
Purchase #5	$171.38	4.670%	$179.3834	$179.38	$179.40	$179.40
Purchase #6	$49.85	9.246%	$54.4591	$54.46	$54.45	$54.50
Purchase #7	$100.37	10.351%	$110.7593	$110.76	$110.75	$110.80
7 purchase totals =	$904.26		$977.1428	$977.15	$977.10	$977.20