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	$6.61	10.835%	$7.3262	$7.33	$7.35	$7.30
Purchase #2	$111.75	7.651%	$120.3	$120.30	$120.30	$120.30
Purchase #3	$138.29	4.424%	$144.4079	$144.41	$144.40	$144.40
Purchase #4	$240.39	6.193%	$255.2774	$255.28	$255.30	$255.30
Purchase #5	$190.97	10.249%	$210.5425	$210.54	$210.55	$210.50
Purchase #6	$184.70	6.509%	$196.7221	$196.72	$196.70	$196.70
Purchase #7	$192.88	10.222%	$212.5962	$212.60	$212.60	$212.60
7 purchase totals =	$1,065.59		$1,147.1723	$1,147.18	$1,147.20	$1,147.10