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	$247.47	13.278%	$280.3291	$280.33	$280.35	$280.30
Purchase #2	$44.58	4.226%	$46.464	$46.46	$46.45	$46.50
Purchase #3	$138.36	11.461%	$154.2174	$154.22	$154.20	$154.20
Purchase #4	$216.67	11.781%	$242.1959	$242.20	$242.20	$242.20
Purchase #5	$77.39	7.114%	$82.8955	$82.90	$82.90	$82.90
Purchase #6	$47.80	5.170%	$50.2713	$50.27	$50.25	$50.30
Purchase #7	$130.93	5.764%	$138.4768	$138.48	$138.50	$138.50
7 purchase totals =	$903.20		$994.8500	$994.86	$994.85	$994.90