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	$80.67	11.645%	$90.064	$90.06	$90.05	$90.10
Purchase #2	$190.81	5.415%	$201.1424	$201.14	$201.15	$201.10
Purchase #3	$198.96	10.137%	$219.1286	$219.13	$219.15	$219.10
Purchase #4	$56.60	4.349%	$59.0615	$59.06	$59.05	$59.10
Purchase #5	$244.70	13.331%	$277.321	$277.32	$277.30	$277.30
Purchase #6	$77.42	6.454%	$82.4167	$82.42	$82.40	$82.40
Purchase #7	$67.67	7.204%	$72.5449	$72.54	$72.55	$72.50
7 purchase totals =	$916.83		$1,001.6791	$1,001.67	$1,001.65	$1,001.60