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	$86.37	4.743%	$90.4665	$90.47	$90.45	$90.50
Purchase #2	$229.76	3.769%	$238.4197	$238.42	$238.40	$238.40
Purchase #3	$177.37	4.219%	$184.8532	$184.85	$184.85	$184.90
Purchase #4	$174.29	12.809%	$196.6148	$196.61	$196.60	$196.60
Purchase #5	$64.83	13.591%	$73.641	$73.64	$73.65	$73.60
Purchase #6	$53.78	9.676%	$58.9838	$58.98	$59.00	$59.00
Purchase #7	$105.76	8.834%	$115.1028	$115.10	$115.10	$115.10
7 purchase totals =	$892.16		$958.0818	$958.07	$958.05	$958.10