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	$243.80	5.839%	$258.0355	$258.04	$258.05	$258.00
Purchase #2	$68.49	4.144%	$71.3282	$71.33	$71.35	$71.30
Purchase #3	$26.64	6.189%	$28.2887	$28.29	$28.30	$28.30
Purchase #4	$173.42	13.110%	$196.1554	$196.16	$196.15	$196.20
Purchase #5	$68.88	5.746%	$72.8378	$72.84	$72.85	$72.80
Purchase #6	$79.75	13.765%	$90.7276	$90.73	$90.75	$90.70
Purchase #7	$98.66	5.331%	$103.9196	$103.92	$103.90	$103.90
7 purchase totals =	$759.64		$821.2928	$821.31	$821.35	$821.20