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	$37.30	4.830%	$39.1016	$39.10	$39.10	$39.10
Purchase #2	$80.98	13.196%	$91.6661	$91.67	$91.65	$91.70
Purchase #3	$234.70	13.558%	$266.5206	$266.52	$266.50	$266.50
Purchase #4	$123.48	4.250%	$128.7279	$128.73	$128.75	$128.70
Purchase #5	$43.55	4.341%	$45.4405	$45.44	$45.45	$45.40
Purchase #6	$136.61	5.687%	$144.379	$144.38	$144.40	$144.40
Purchase #7	$186.34	11.406%	$207.5939	$207.59	$207.60	$207.60
7 purchase totals =	$842.96		$923.4296	$923.43	$923.45	$923.40