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	$85.35	5.243%	$89.8249	$89.82	$89.80	$89.80
Purchase #2	$84.75	5.601%	$89.4968	$89.50	$89.50	$89.50
Purchase #3	$167.42	4.259%	$174.5504	$174.55	$174.55	$174.60
Purchase #4	$231.49	11.138%	$257.2734	$257.27	$257.25	$257.30
Purchase #5	$42.44	8.720%	$46.1408	$46.14	$46.15	$46.10
Purchase #6	$181.88	7.397%	$195.3337	$195.33	$195.35	$195.30
Purchase #7	$233.47	6.354%	$248.3047	$248.30	$248.30	$248.30
7 purchase totals =	$1,026.80		$1,100.9247	$1,100.91	$1,100.90	$1,100.90