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	$248.73	7.348%	$267.0067	$267.01	$267.00	$267.00
Purchase #2	$72.46	9.460%	$79.3147	$79.31	$79.30	$79.30
Purchase #3	$44.87	5.346%	$47.2688	$47.27	$47.25	$47.30
Purchase #4	$119.89	6.284%	$127.4239	$127.42	$127.40	$127.40
Purchase #5	$62.79	13.559%	$71.3037	$71.30	$71.30	$71.30
Purchase #6	$241.70	9.758%	$265.2851	$265.29	$265.30	$265.30
Purchase #7	$94.71	4.799%	$99.2551	$99.26	$99.25	$99.30
7 purchase totals =	$885.15		$956.8580	$956.86	$956.80	$956.90