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	$236.41	13.372%	$268.0227	$268.02	$268.00	$268.00
Purchase #2	$85.90	9.577%	$94.1266	$94.13	$94.15	$94.10
Purchase #3	$111.41	11.813%	$124.5709	$124.57	$124.55	$124.60
Purchase #4	$91.98	13.486%	$104.3844	$104.38	$104.40	$104.40
Purchase #5	$30.41	8.160%	$32.8915	$32.89	$32.90	$32.90
Purchase #6	$133.78	7.364%	$143.6316	$143.63	$143.65	$143.60
Purchase #7	$80.45	6.761%	$85.8892	$85.89	$85.90	$85.90
7 purchase totals =	$770.34		$853.5169	$853.51	$853.55	$853.50