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	$81.63	10.320%	$90.0542	$90.05	$90.05	$90.10
Purchase #2	$38.65	9.157%	$42.1892	$42.19	$42.20	$42.20
Purchase #3	$57.44	10.596%	$63.5263	$63.53	$63.55	$63.50
Purchase #4	$74.63	9.507%	$81.7251	$81.73	$81.75	$81.70
Purchase #5	$173.94	4.140%	$181.1411	$181.14	$181.15	$181.10
Purchase #6	$93.39	12.721%	$105.2701	$105.27	$105.25	$105.30
Purchase #7	$28.32	11.451%	$31.5629	$31.56	$31.55	$31.60
7 purchase totals =	$548.00		$595.4689	$595.47	$595.50	$595.50