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	$160.48	5.173%	$168.7816	$168.78	$168.80	$168.80
Purchase #2	$181.76	5.822%	$192.3421	$192.34	$192.35	$192.30
Purchase #3	$92.89	13.144%	$105.0995	$105.10	$105.10	$105.10
Purchase #4	$178.26	3.622%	$184.7166	$184.72	$184.70	$184.70
Purchase #5	$237.50	8.833%	$258.4784	$258.48	$258.50	$258.50
Purchase #6	$118.27	7.421%	$127.0468	$127.05	$127.05	$127.00
Purchase #7	$221.69	12.486%	$249.3702	$249.37	$249.35	$249.40
7 purchase totals =	$1,190.85		$1,285.8352	$1,285.84	$1,285.85	$1,285.80