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	$27.66	8.766%	$30.0847	$30.08	$30.10	$30.10
Purchase #2	$39.40	7.657%	$42.4169	$42.42	$42.40	$42.40
Purchase #3	$65.30	3.127%	$67.3419	$67.34	$67.35	$67.30
Purchase #4	$229.77	8.562%	$249.4429	$249.44	$249.45	$249.40
Purchase #5	$6.63	5.251%	$6.9781	$6.98	$7.00	$7.00
Purchase #6	$69.33	12.858%	$78.2445	$78.24	$78.25	$78.20
Purchase #7	$158.77	10.788%	$175.8981	$175.90	$175.90	$175.90
7 purchase totals =	$596.86		$650.4071	$650.40	$650.45	$650.30