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	$132.59	13.138%	$150.0097	$150.01	$150.00	$150.00
Purchase #2	$155.71	6.148%	$165.2831	$165.28	$165.30	$165.30
Purchase #3	$181.79	4.173%	$189.3761	$189.38	$189.40	$189.40
Purchase #4	$204.88	12.406%	$230.2974	$230.30	$230.30	$230.30
Purchase #5	$184.47	6.705%	$196.8387	$196.84	$196.85	$196.80
Purchase #6	$36.71	6.172%	$38.9757	$38.98	$39.00	$39.00
Purchase #7	$230.70	8.504%	$250.3187	$250.32	$250.30	$250.30
7 purchase totals =	$1,126.85		$1,221.0994	$1,221.11	$1,221.15	$1,221.10