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	$6.58	11.254%	$7.3205	$7.32	$7.30	$7.30
Purchase #2	$227.64	11.265%	$253.2836	$253.28	$253.30	$253.30
Purchase #3	$66.38	9.566%	$72.7299	$72.73	$72.75	$72.70
Purchase #4	$38.52	12.362%	$43.2818	$43.28	$43.30	$43.30
Purchase #5	$143.48	9.288%	$156.8064	$156.81	$156.80	$156.80
Purchase #6	$85.70	9.823%	$94.1183	$94.12	$94.10	$94.10
Purchase #7	$163.69	6.165%	$173.7815	$173.78	$173.80	$173.80
7 purchase totals =	$731.99		$801.3220	$801.32	$801.35	$801.30