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	$155.40	6.354%	$165.2741	$165.27	$165.25	$165.30
Purchase #2	$236.64	4.238%	$246.6688	$246.67	$246.65	$246.70
Purchase #3	$212.83	5.779%	$225.1294	$225.13	$225.15	$225.10
Purchase #4	$64.26	12.678%	$72.4069	$72.41	$72.40	$72.40
Purchase #5	$18.42	9.234%	$20.1209	$20.12	$20.10	$20.10
Purchase #6	$44.64	13.245%	$50.5526	$50.55	$50.55	$50.60
Purchase #7	$156.60	3.849%	$162.6275	$162.63	$162.65	$162.60
7 purchase totals =	$888.79		$942.7802	$942.78	$942.75	$942.80