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	$99.72	3.234%	$102.9449	$102.94	$102.95	$102.90
Purchase #2	$69.83	12.604%	$78.6314	$78.63	$78.65	$78.60
Purchase #3	$225.37	8.391%	$244.2808	$244.28	$244.30	$244.30
Purchase #4	$99.32	7.778%	$107.0451	$107.05	$107.05	$107.00
Purchase #5	$175.80	5.559%	$185.5727	$185.57	$185.55	$185.60
Purchase #6	$135.37	5.732%	$143.1294	$143.13	$143.15	$143.10
Purchase #7	$178.40	4.114%	$185.7394	$185.74	$185.75	$185.70
7 purchase totals =	$983.81		$1,047.3437	$1,047.34	$1,047.40	$1,047.20