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	$122.32	7.862%	$131.9368	$131.94	$131.95	$131.90
Purchase #2	$67.28	4.669%	$70.4213	$70.42	$70.40	$70.40
Purchase #3	$31.64	3.787%	$32.8382	$32.84	$32.85	$32.80
Purchase #4	$46.27	9.828%	$50.8174	$50.82	$50.80	$50.80
Purchase #5	$39.88	5.769%	$42.1807	$42.18	$42.20	$42.20
Purchase #6	$38.92	3.639%	$40.3363	$40.34	$40.35	$40.30
Purchase #7	$243.62	6.373%	$259.1459	$259.15	$259.15	$259.10
7 purchase totals =	$589.93		$627.6766	$627.69	$627.70	$627.50