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	$199.50	8.644%	$216.7448	$216.74	$216.75	$216.70
Purchase #2	$162.49	10.168%	$179.012	$179.01	$179.00	$179.00
Purchase #3	$50.83	7.167%	$54.473	$54.47	$54.45	$54.50
Purchase #4	$162.94	9.473%	$178.3753	$178.38	$178.40	$178.40
Purchase #5	$59.56	13.280%	$67.4696	$67.47	$67.45	$67.50
Purchase #6	$114.93	5.186%	$120.8903	$120.89	$120.90	$120.90
Purchase #7	$36.78	10.690%	$40.7118	$40.71	$40.70	$40.70
7 purchase totals =	$787.03		$857.6768	$857.67	$857.65	$857.70