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	$157.87	12.385%	$177.4222	$177.42	$177.40	$177.40
Purchase #2	$115.78	9.693%	$127.0026	$127.00	$127.00	$127.00
Purchase #3	$141.90	4.725%	$148.6048	$148.60	$148.60	$148.60
Purchase #4	$165.60	11.306%	$184.3227	$184.32	$184.30	$184.30
Purchase #5	$211.54	5.641%	$223.473	$223.47	$223.45	$223.50
Purchase #6	$174.44	4.549%	$182.3753	$182.38	$182.40	$182.40
Purchase #7	$206.90	13.773%	$235.3963	$235.40	$235.40	$235.40
7 purchase totals =	$1,174.03		$1,278.5969	$1,278.59	$1,278.55	$1,278.60