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	$92.73	10.562%	$102.5241	$102.52	$102.50	$102.50
Purchase #2	$235.77	12.529%	$265.3096	$265.31	$265.30	$265.30
Purchase #3	$206.54	10.555%	$228.3403	$228.34	$228.35	$228.30
Purchase #4	$224.60	10.126%	$247.343	$247.34	$247.35	$247.30
Purchase #5	$41.73	8.854%	$45.4248	$45.42	$45.40	$45.40
Purchase #6	$140.51	11.362%	$156.4747	$156.47	$156.45	$156.50
Purchase #7	$75.72	9.258%	$82.7302	$82.73	$82.75	$82.70
7 purchase totals =	$1,017.60		$1,128.1467	$1,128.13	$1,128.10	$1,128.00