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	$130.59	13.120%	$147.7234	$147.72	$147.70	$147.70
Purchase #2	$54.87	7.757%	$59.1263	$59.13	$59.15	$59.10
Purchase #3	$243.73	8.624%	$264.7493	$264.75	$264.75	$264.70
Purchase #4	$28.98	10.668%	$32.0716	$32.07	$32.05	$32.10
Purchase #5	$245.67	13.412%	$278.6193	$278.62	$278.60	$278.60
Purchase #6	$114.77	7.577%	$123.4661	$123.47	$123.45	$123.50
Purchase #7	$103.31	11.225%	$114.9065	$114.91	$114.90	$114.90
7 purchase totals =	$921.92		$1,020.6625	$1,020.67	$1,020.60	$1,020.60