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	$10.28	8.541%	$11.158	$11.16	$11.15	$11.20
Purchase #2	$178.97	8.801%	$194.7211	$194.72	$194.70	$194.70
Purchase #3	$170.44	8.834%	$185.4967	$185.50	$185.50	$185.50
Purchase #4	$56.33	6.269%	$59.8613	$59.86	$59.85	$59.90
Purchase #5	$247.85	13.273%	$280.7471	$280.75	$280.75	$280.70
Purchase #6	$98.90	6.314%	$105.1445	$105.14	$105.15	$105.10
Purchase #7	$47.78	8.518%	$51.8499	$51.85	$51.85	$51.80
7 purchase totals =	$810.55		$888.9786	$888.98	$888.95	$888.90