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	$134.87	6.417%	$143.5246	$143.52	$143.50	$143.50
Purchase #2	$80.63	10.635%	$89.205	$89.21	$89.20	$89.20
Purchase #3	$146.84	7.618%	$158.0263	$158.03	$158.05	$158.00
Purchase #4	$131.71	9.610%	$144.3673	$144.37	$144.35	$144.40
Purchase #5	$140.54	12.677%	$158.3563	$158.36	$158.35	$158.40
Purchase #6	$9.93	12.345%	$11.1559	$11.16	$11.15	$11.20
Purchase #7	$229.28	6.356%	$243.853	$243.85	$243.85	$243.90
7 purchase totals =	$873.80		$948.4884	$948.50	$948.45	$948.60