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	$101.64	8.821%	$110.6057	$110.61	$110.60	$110.60
Purchase #2	$85.92	4.289%	$89.6051	$89.61	$89.60	$89.60
Purchase #3	$16.61	9.357%	$18.1642	$18.16	$18.15	$18.20
Purchase #4	$238.44	12.687%	$268.6909	$268.69	$268.70	$268.70
Purchase #5	$203.28	8.643%	$220.8495	$220.85	$220.85	$220.80
Purchase #6	$116.36	13.374%	$131.922	$131.92	$131.90	$131.90
Purchase #7	$223.46	11.638%	$249.4663	$249.47	$249.45	$249.50
7 purchase totals =	$985.71		$1,089.3037	$1,089.31	$1,089.25	$1,089.30