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	$38.45	6.376%	$40.9016	$40.90	$40.90	$40.90
Purchase #2	$58.86	8.519%	$63.8743	$63.87	$63.85	$63.90
Purchase #3	$83.52	13.828%	$95.0691	$95.07	$95.05	$95.10
Purchase #4	$7.36	7.395%	$7.9043	$7.90	$7.90	$7.90
Purchase #5	$90.74	9.207%	$99.0944	$99.09	$99.10	$99.10
Purchase #6	$175.75	7.221%	$188.4409	$188.44	$188.45	$188.40
Purchase #7	$88.74	8.248%	$96.0593	$96.06	$96.05	$96.10
7 purchase totals =	$543.42		$591.3439	$591.33	$591.30	$591.40