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	$108.73	6.269%	$115.5463	$115.55	$115.55	$115.50
Purchase #2	$97.94	3.821%	$101.6823	$101.68	$101.70	$101.70
Purchase #3	$73.41	10.726%	$81.284	$81.28	$81.30	$81.30
Purchase #4	$227.42	12.446%	$255.7247	$255.72	$255.70	$255.70
Purchase #5	$171.88	9.333%	$187.9216	$187.92	$187.90	$187.90
Purchase #6	$102.43	11.783%	$114.4993	$114.50	$114.50	$114.50
Purchase #7	$98.62	13.132%	$111.5708	$111.57	$111.55	$111.60
7 purchase totals =	$880.43		$968.2290	$968.22	$968.20	$968.20