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	$158.81	9.768%	$174.3226	$174.32	$174.30	$174.30
Purchase #2	$239.82	12.221%	$269.1284	$269.13	$269.15	$269.10
Purchase #3	$249.47	8.480%	$270.6251	$270.63	$270.65	$270.60
Purchase #4	$190.68	11.827%	$213.2317	$213.23	$213.25	$213.20
Purchase #5	$77.58	6.867%	$82.9074	$82.91	$82.90	$82.90
Purchase #6	$150.79	10.789%	$167.0587	$167.06	$167.05	$167.10
Purchase #7	$51.30	11.658%	$57.2806	$57.28	$57.30	$57.30
7 purchase totals =	$1,118.45		$1,234.5545	$1,234.56	$1,234.60	$1,234.50