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	$173.79	8.440%	$188.4579	$188.46	$188.45	$188.50
Purchase #2	$77.81	6.870%	$83.1555	$83.16	$83.15	$83.20
Purchase #3	$37.69	4.664%	$39.4479	$39.45	$39.45	$39.40
Purchase #4	$209.64	6.416%	$223.0905	$223.09	$223.10	$223.10
Purchase #5	$232.70	3.291%	$240.3582	$240.36	$240.35	$240.40
Purchase #6	$108.63	13.603%	$123.4069	$123.41	$123.40	$123.40
Purchase #7	$169.87	12.817%	$191.6422	$191.64	$191.65	$191.60
7 purchase totals =	$1,010.13		$1,089.5591	$1,089.57	$1,089.55	$1,089.60