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	$120.49	8.710%	$130.9847	$130.98	$131.00	$131.00
Purchase #2	$146.83	4.479%	$153.4065	$153.41	$153.40	$153.40
Purchase #3	$175.98	8.484%	$190.9101	$190.91	$190.90	$190.90
Purchase #4	$238.80	6.313%	$253.8754	$253.88	$253.90	$253.90
Purchase #5	$249.91	10.809%	$276.9228	$276.92	$276.90	$276.90
Purchase #6	$195.75	11.426%	$218.1164	$218.12	$218.10	$218.10
Purchase #7	$68.72	11.135%	$76.372	$76.37	$76.35	$76.40
7 purchase totals =	$1,196.48		$1,300.5879	$1,300.59	$1,300.55	$1,300.60