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	$170.32	9.817%	$187.0403	$187.04	$187.05	$187.00
Purchase #2	$72.94	10.375%	$80.5075	$80.51	$80.50	$80.50
Purchase #3	$151.41	3.629%	$156.9047	$156.90	$156.90	$156.90
Purchase #4	$53.56	11.107%	$59.5089	$59.51	$59.50	$59.50
Purchase #5	$214.64	7.632%	$231.0213	$231.02	$231.00	$231.00
Purchase #6	$129.42	6.131%	$137.3547	$137.35	$137.35	$137.40
Purchase #7	$56.50	13.233%	$63.9766	$63.98	$64.00	$64.00
7 purchase totals =	$848.79		$916.3140	$916.31	$916.30	$916.30