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	$165.87	11.714%	$185.3	$185.30	$185.30	$185.30
Purchase #2	$184.40	6.661%	$196.6829	$196.68	$196.70	$196.70
Purchase #3	$46.81	6.817%	$50.001	$50.00	$50.00	$50.00
Purchase #4	$145.81	10.206%	$160.6914	$160.69	$160.70	$160.70
Purchase #5	$15.54	11.382%	$17.3088	$17.31	$17.30	$17.30
Purchase #6	$237.68	11.446%	$264.8849	$264.88	$264.90	$264.90
Purchase #7	$23.28	8.148%	$25.1769	$25.18	$25.20	$25.20
7 purchase totals =	$819.39		$900.0459	$900.04	$900.10	$900.10