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	$57.48	9.597%	$62.9964	$63.00	$63.00	$63.00
Purchase #2	$238.29	4.494%	$248.9988	$249.00	$249.00	$249.00
Purchase #3	$110.98	5.708%	$117.3147	$117.31	$117.30	$117.30
Purchase #4	$204.76	8.592%	$222.353	$222.35	$222.35	$222.40
Purchase #5	$49.96	12.310%	$56.1101	$56.11	$56.10	$56.10
Purchase #6	$96.86	8.528%	$105.1202	$105.12	$105.10	$105.10
Purchase #7	$89.27	12.659%	$100.5707	$100.57	$100.55	$100.60
7 purchase totals =	$847.60		$913.4639	$913.46	$913.40	$913.50