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	$136.87	6.404%	$145.6352	$145.64	$145.65	$145.60
Purchase #2	$180.61	4.790%	$189.2612	$189.26	$189.25	$189.30
Purchase #3	$43.46	9.665%	$47.6604	$47.66	$47.65	$47.70
Purchase #4	$76.28	7.840%	$82.2604	$82.26	$82.25	$82.30
Purchase #5	$45.33	4.278%	$47.2692	$47.27	$47.25	$47.30
Purchase #6	$117.53	5.439%	$123.9225	$123.92	$123.90	$123.90
Purchase #7	$92.67	6.572%	$98.7603	$98.76	$98.75	$98.80
7 purchase totals =	$692.75		$734.7692	$734.77	$734.70	$734.90