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	$134.90	12.308%	$151.5035	$151.50	$151.50	$151.50
Purchase #2	$145.57	10.796%	$161.2857	$161.29	$161.30	$161.30
Purchase #3	$97.51	9.114%	$106.3971	$106.40	$106.40	$106.40
Purchase #4	$74.80	10.740%	$82.8335	$82.83	$82.85	$82.80
Purchase #5	$148.41	6.161%	$157.5535	$157.55	$157.55	$157.60
Purchase #6	$132.78	4.179%	$138.3289	$138.33	$138.35	$138.30
Purchase #7	$196.98	13.645%	$223.8579	$223.86	$223.85	$223.90
7 purchase totals =	$930.95		$1,021.7601	$1,021.76	$1,021.80	$1,021.80