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	$39.83	7.575%	$42.8471	$42.85	$42.85	$42.80
Purchase #2	$236.27	6.550%	$251.7457	$251.75	$251.75	$251.70
Purchase #3	$203.34	5.763%	$215.0585	$215.06	$215.05	$215.10
Purchase #4	$218.83	6.142%	$232.2705	$232.27	$232.25	$232.30
Purchase #5	$104.94	4.715%	$109.8879	$109.89	$109.90	$109.90
Purchase #6	$143.48	10.825%	$159.0117	$159.01	$159.00	$159.00
Purchase #7	$74.25	7.184%	$79.5841	$79.58	$79.60	$79.60
7 purchase totals =	$1,020.94		$1,090.4055	$1,090.41	$1,090.40	$1,090.40