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	$179.44	9.617%	$196.6967	$196.70	$196.70	$196.70
Purchase #2	$11.53	11.259%	$12.8282	$12.83	$12.85	$12.80
Purchase #3	$125.30	3.765%	$130.0175	$130.02	$130.00	$130.00
Purchase #4	$5.97	10.400%	$6.5909	$6.59	$6.60	$6.60
Purchase #5	$72.82	11.594%	$81.2628	$81.26	$81.25	$81.30
Purchase #6	$158.41	13.144%	$179.2314	$179.23	$179.25	$179.20
Purchase #7	$31.78	5.512%	$33.5317	$33.53	$33.55	$33.50
7 purchase totals =	$585.25		$640.1592	$640.16	$640.20	$640.10