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	$136.58	5.643%	$144.2872	$144.29	$144.30	$144.30
Purchase #2	$191.32	7.208%	$205.1103	$205.11	$205.10	$205.10
Purchase #3	$81.55	10.141%	$89.82	$89.82	$89.80	$89.80
Purchase #4	$99.30	7.830%	$107.0752	$107.08	$107.10	$107.10
Purchase #5	$61.97	10.616%	$68.5487	$68.55	$68.55	$68.50
Purchase #6	$123.28	6.562%	$131.3696	$131.37	$131.35	$131.40
Purchase #7	$190.56	3.842%	$197.8813	$197.88	$197.90	$197.90
7 purchase totals =	$884.56		$944.0923	$944.10	$944.10	$944.10