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	$157.85	7.758%	$170.096	$170.10	$170.10	$170.10
Purchase #2	$210.46	10.517%	$232.5941	$232.59	$232.60	$232.60
Purchase #3	$184.98	6.145%	$196.347	$196.35	$196.35	$196.30
Purchase #4	$144.35	7.554%	$155.2542	$155.25	$155.25	$155.30
Purchase #5	$71.45	12.361%	$80.2819	$80.28	$80.30	$80.30
Purchase #6	$203.25	9.345%	$222.2437	$222.24	$222.25	$222.20
Purchase #7	$145.36	11.534%	$162.1258	$162.13	$162.15	$162.10
7 purchase totals =	$1,117.70		$1,218.9427	$1,218.94	$1,219.00	$1,218.90