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	$37.48	6.323%	$39.8499	$39.85	$39.85	$39.80
Purchase #2	$42.71	10.297%	$47.1078	$47.11	$47.10	$47.10
Purchase #3	$59.43	5.241%	$62.5447	$62.54	$62.55	$62.50
Purchase #4	$164.41	10.445%	$181.5826	$181.58	$181.60	$181.60
Purchase #5	$190.30	3.369%	$196.7112	$196.71	$196.70	$196.70
Purchase #6	$39.28	3.446%	$40.6336	$40.63	$40.65	$40.60
Purchase #7	$171.76	10.278%	$189.4135	$189.41	$189.40	$189.40
7 purchase totals =	$705.37		$757.8433	$757.83	$757.85	$757.70