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	$244.75	5.759%	$258.8452	$258.85	$258.85	$258.80
Purchase #2	$79.63	3.183%	$82.1646	$82.16	$82.15	$82.20
Purchase #3	$56.89	8.341%	$61.6352	$61.64	$61.65	$61.60
Purchase #4	$103.85	9.221%	$113.426	$113.43	$113.45	$113.40
Purchase #5	$38.78	12.859%	$43.7667	$43.77	$43.75	$43.80
Purchase #6	$210.46	6.220%	$223.5506	$223.55	$223.55	$223.60
Purchase #7	$201.88	4.516%	$210.9969	$211.00	$211.00	$211.00
7 purchase totals =	$936.24		$994.3852	$994.40	$994.40	$994.40