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	$90.52	8.780%	$98.4677	$98.47	$98.45	$98.50
Purchase #2	$93.64	12.650%	$105.4855	$105.49	$105.50	$105.50
Purchase #3	$84.43	8.173%	$91.3305	$91.33	$91.35	$91.30
Purchase #4	$142.60	5.478%	$150.4116	$150.41	$150.40	$150.40
Purchase #5	$230.69	13.548%	$261.9439	$261.94	$261.95	$261.90
Purchase #6	$50.30	10.504%	$55.5835	$55.58	$55.60	$55.60
Purchase #7	$54.61	9.235%	$59.6532	$59.65	$59.65	$59.70
7 purchase totals =	$746.79		$822.8759	$822.87	$822.90	$822.90