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	$174.98	8.550%	$189.9408	$189.94	$189.95	$189.90
Purchase #2	$165.66	9.423%	$181.2701	$181.27	$181.25	$181.30
Purchase #3	$234.74	12.275%	$263.5543	$263.55	$263.55	$263.60
Purchase #4	$233.73	11.266%	$260.062	$260.06	$260.05	$260.10
Purchase #5	$108.88	13.148%	$123.1955	$123.20	$123.20	$123.20
Purchase #6	$44.60	4.329%	$46.5307	$46.53	$46.55	$46.50
Purchase #7	$164.85	12.634%	$185.6771	$185.68	$185.70	$185.70
7 purchase totals =	$1,127.44		$1,250.2305	$1,250.23	$1,250.25	$1,250.30