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	$186.97	12.564%	$210.4609	$210.46	$210.45	$210.50
Purchase #2	$95.32	6.718%	$101.7236	$101.72	$101.70	$101.70
Purchase #3	$74.78	10.623%	$82.7239	$82.72	$82.70	$82.70
Purchase #4	$157.38	4.475%	$164.4228	$164.42	$164.40	$164.40
Purchase #5	$54.63	12.322%	$61.3615	$61.36	$61.35	$61.40
Purchase #6	$38.75	8.167%	$41.9147	$41.91	$41.90	$41.90
Purchase #7	$145.51	6.272%	$154.6364	$154.64	$154.65	$154.60
7 purchase totals =	$753.34		$817.2438	$817.23	$817.15	$817.20