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	$222.73	12.166%	$249.8273	$249.83	$249.85	$249.80
Purchase #2	$163.59	9.385%	$178.9429	$178.94	$178.95	$178.90
Purchase #3	$102.30	13.536%	$116.1473	$116.15	$116.15	$116.10
Purchase #4	$185.78	12.517%	$209.0341	$209.03	$209.05	$209.00
Purchase #5	$246.52	7.383%	$264.7206	$264.72	$264.70	$264.70
Purchase #6	$93.27	6.170%	$99.0248	$99.02	$99.00	$99.00
Purchase #7	$95.33	6.836%	$101.8468	$101.85	$101.85	$101.80
7 purchase totals =	$1,109.52		$1,219.5438	$1,219.54	$1,219.55	$1,219.30