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	$91.35	10.168%	$100.6385	$100.64	$100.65	$100.60
Purchase #2	$37.37	4.476%	$39.0427	$39.04	$39.05	$39.00
Purchase #3	$136.41	6.428%	$145.1784	$145.18	$145.20	$145.20
Purchase #4	$167.40	8.613%	$181.8182	$181.82	$181.80	$181.80
Purchase #5	$99.25	6.736%	$105.9355	$105.94	$105.95	$105.90
Purchase #6	$209.54	11.523%	$233.6853	$233.69	$233.70	$233.70
Purchase #7	$170.99	11.237%	$190.2041	$190.20	$190.20	$190.20
7 purchase totals =	$912.31		$996.5027	$996.51	$996.55	$996.40