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	$240.31	4.266%	$250.5616	$250.56	$250.55	$250.60
Purchase #2	$72.36	12.572%	$81.4571	$81.46	$81.45	$81.50
Purchase #3	$54.70	12.256%	$61.404	$61.40	$61.40	$61.40
Purchase #4	$205.67	12.262%	$230.8893	$230.89	$230.90	$230.90
Purchase #5	$18.77	4.266%	$19.5707	$19.57	$19.55	$19.60
Purchase #6	$90.28	9.370%	$98.7392	$98.74	$98.75	$98.70
Purchase #7	$64.77	3.207%	$66.8472	$66.85	$66.85	$66.80
7 purchase totals =	$746.86		$809.4691	$809.47	$809.45	$809.50