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	$134.37	6.838%	$143.5582	$143.56	$143.55	$143.60
Purchase #2	$78.90	9.704%	$86.5565	$86.56	$86.55	$86.60
Purchase #3	$117.66	11.140%	$130.7673	$130.77	$130.75	$130.80
Purchase #4	$205.70	6.650%	$219.3791	$219.38	$219.40	$219.40
Purchase #5	$171.42	5.663%	$181.1275	$181.13	$181.15	$181.10
Purchase #6	$192.76	3.157%	$198.8454	$198.85	$198.85	$198.80
Purchase #7	$188.97	12.518%	$212.6253	$212.63	$212.65	$212.60
7 purchase totals =	$1,089.78		$1,172.8593	$1,172.88	$1,172.90	$1,172.90