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	$103.65	8.518%	$112.4789	$112.48	$112.50	$112.50
Purchase #2	$188.33	10.236%	$207.6075	$207.61	$207.60	$207.60
Purchase #3	$44.65	12.620%	$50.2848	$50.28	$50.30	$50.30
Purchase #4	$37.45	11.113%	$41.6118	$41.61	$41.60	$41.60
Purchase #5	$168.89	4.164%	$175.9226	$175.92	$175.90	$175.90
Purchase #6	$228.48	4.518%	$238.8027	$238.80	$238.80	$238.80
Purchase #7	$47.27	9.550%	$51.7843	$51.78	$51.80	$51.80
7 purchase totals =	$818.72		$878.4926	$878.48	$878.50	$878.50