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	$115.25	13.454%	$130.7557	$130.76	$130.75	$130.80
Purchase #2	$103.73	10.156%	$114.2648	$114.26	$114.25	$114.30
Purchase #3	$175.47	3.399%	$181.4342	$181.43	$181.45	$181.40
Purchase #4	$80.46	11.339%	$89.5834	$89.58	$89.60	$89.60
Purchase #5	$71.90	11.641%	$80.2699	$80.27	$80.25	$80.30
Purchase #6	$19.86	13.597%	$22.5604	$22.56	$22.55	$22.60
Purchase #7	$156.66	10.791%	$173.5652	$173.57	$173.55	$173.60
7 purchase totals =	$723.33		$792.4336	$792.43	$792.40	$792.60