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	$248.93	4.363%	$259.7908	$259.79	$259.80	$259.80
Purchase #2	$209.56	3.776%	$217.473	$217.47	$217.45	$217.50
Purchase #3	$214.46	3.764%	$222.5323	$222.53	$222.55	$222.50
Purchase #4	$50.65	5.279%	$53.3238	$53.32	$53.30	$53.30
Purchase #5	$249.61	3.871%	$259.2724	$259.27	$259.25	$259.30
Purchase #6	$194.37	4.808%	$203.7153	$203.72	$203.70	$203.70
Purchase #7	$72.76	12.675%	$81.9823	$81.98	$82.00	$82.00
7 purchase totals =	$1,240.34		$1,298.0899	$1,298.08	$1,298.05	$1,298.10