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	$124.42	7.736%	$134.0451	$134.05	$134.05	$134.00
Purchase #2	$157.42	10.818%	$174.4497	$174.45	$174.45	$174.40
Purchase #3	$94.42	10.655%	$104.4805	$104.48	$104.50	$104.50
Purchase #4	$238.98	6.868%	$255.3931	$255.39	$255.40	$255.40
Purchase #5	$77.52	8.680%	$84.2487	$84.25	$84.25	$84.20
Purchase #6	$102.83	8.482%	$111.552	$111.55	$111.55	$111.60
Purchase #7	$206.33	9.488%	$225.9066	$225.91	$225.90	$225.90
7 purchase totals =	$1,001.92		$1,090.0757	$1,090.08	$1,090.10	$1,090.00