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	$228.87	10.762%	$253.501	$253.50	$253.50	$253.50
Purchase #2	$165.56	5.260%	$174.2685	$174.27	$174.25	$174.30
Purchase #3	$90.32	7.742%	$97.3126	$97.31	$97.30	$97.30
Purchase #4	$85.96	11.553%	$95.891	$95.89	$95.90	$95.90
Purchase #5	$103.77	4.687%	$108.6337	$108.63	$108.65	$108.60
Purchase #6	$28.51	13.442%	$32.3423	$32.34	$32.35	$32.30
Purchase #7	$46.86	13.234%	$53.0615	$53.06	$53.05	$53.10
7 purchase totals =	$749.85		$815.0106	$815.00	$815.00	$815.00