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	$93.42	6.736%	$99.7128	$99.71	$99.70	$99.70
Purchase #2	$246.25	4.159%	$256.4915	$256.49	$256.50	$256.50
Purchase #3	$100.64	9.349%	$110.0488	$110.05	$110.05	$110.00
Purchase #4	$81.79	4.808%	$85.7225	$85.72	$85.70	$85.70
Purchase #5	$249.85	9.415%	$273.3734	$273.37	$273.35	$273.40
Purchase #6	$203.58	5.337%	$214.4451	$214.45	$214.45	$214.40
Purchase #7	$29.65	7.320%	$31.8204	$31.82	$31.80	$31.80
7 purchase totals =	$1,005.18		$1,071.6145	$1,071.61	$1,071.55	$1,071.50