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	$221.89	5.130%	$233.273	$233.27	$233.25	$233.30
Purchase #2	$205.42	13.181%	$232.4964	$232.50	$232.50	$232.50
Purchase #3	$103.78	6.523%	$110.5496	$110.55	$110.55	$110.50
Purchase #4	$76.95	12.131%	$86.2848	$86.28	$86.30	$86.30
Purchase #5	$137.48	6.113%	$145.8842	$145.88	$145.90	$145.90
Purchase #6	$36.79	7.755%	$39.6431	$39.64	$39.65	$39.60
Purchase #7	$119.96	8.755%	$130.4625	$130.46	$130.45	$130.50
7 purchase totals =	$902.27		$978.5936	$978.58	$978.60	$978.60