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	$217.73	9.667%	$238.778	$238.78	$238.80	$238.80
Purchase #2	$243.89	10.798%	$270.2252	$270.23	$270.25	$270.20
Purchase #3	$92.39	9.147%	$100.8409	$100.84	$100.85	$100.80
Purchase #4	$142.63	11.390%	$158.8756	$158.88	$158.90	$158.90
Purchase #5	$119.67	10.432%	$132.154	$132.15	$132.15	$132.20
Purchase #6	$177.56	4.616%	$185.7562	$185.76	$185.75	$185.80
Purchase #7	$216.35	7.685%	$232.9765	$232.98	$233.00	$233.00
7 purchase totals =	$1,210.22		$1,319.6064	$1,319.62	$1,319.70	$1,319.70