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	$155.56	4.394%	$162.3953	$162.40	$162.40	$162.40
Purchase #2	$229.32	11.858%	$256.5128	$256.51	$256.50	$256.50
Purchase #3	$46.64	8.418%	$50.5662	$50.57	$50.55	$50.60
Purchase #4	$156.56	3.722%	$162.3872	$162.39	$162.40	$162.40
Purchase #5	$248.36	11.305%	$276.4371	$276.44	$276.45	$276.40
Purchase #6	$102.54	11.610%	$114.4449	$114.44	$114.45	$114.40
Purchase #7	$250.81	9.872%	$275.57	$275.57	$275.55	$275.60
7 purchase totals =	$1,189.79		$1,298.3135	$1,298.32	$1,298.30	$1,298.30