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	$210.33	6.616%	$224.2454	$224.25	$224.25	$224.20
Purchase #2	$129.32	7.819%	$139.4315	$139.43	$139.45	$139.40
Purchase #3	$25.30	12.430%	$28.4448	$28.44	$28.45	$28.40
Purchase #4	$61.28	10.814%	$67.9068	$67.91	$67.90	$67.90
Purchase #5	$167.95	12.497%	$188.9387	$188.94	$188.95	$188.90
Purchase #6	$129.98	8.569%	$141.118	$141.12	$141.10	$141.10
Purchase #7	$160.34	3.580%	$166.0802	$166.08	$166.10	$166.10
7 purchase totals =	$884.50		$956.1654	$956.17	$956.20	$956.00