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	$25.29	10.368%	$27.9121	$27.91	$27.90	$27.90
Purchase #2	$211.29	5.415%	$222.7314	$222.73	$222.75	$222.70
Purchase #3	$17.47	10.119%	$19.2378	$19.24	$19.25	$19.20
Purchase #4	$99.50	6.214%	$105.6829	$105.68	$105.70	$105.70
Purchase #5	$74.77	6.633%	$79.7295	$79.73	$79.75	$79.70
Purchase #6	$123.59	12.700%	$139.2859	$139.29	$139.30	$139.30
Purchase #7	$87.40	13.683%	$99.3589	$99.36	$99.35	$99.40
7 purchase totals =	$639.31		$693.9385	$693.94	$694.00	$693.90