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	$189.88	13.403%	$215.3296	$215.33	$215.35	$215.30
Purchase #2	$187.79	12.705%	$211.6487	$211.65	$211.65	$211.60
Purchase #3	$230.75	4.383%	$240.8638	$240.86	$240.85	$240.90
Purchase #4	$152.79	12.506%	$171.8979	$171.90	$171.90	$171.90
Purchase #5	$219.50	9.505%	$240.3635	$240.36	$240.35	$240.40
Purchase #6	$168.36	13.152%	$190.5027	$190.50	$190.50	$190.50
Purchase #7	$220.25	4.480%	$230.1172	$230.12	$230.10	$230.10
7 purchase totals =	$1,369.32		$1,500.7234	$1,500.72	$1,500.70	$1,500.70