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	$133.30	3.700%	$138.2321	$138.23	$138.25	$138.20
Purchase #2	$102.27	3.104%	$105.4445	$105.44	$105.45	$105.40
Purchase #3	$233.71	10.740%	$258.8105	$258.81	$258.80	$258.80
Purchase #4	$194.90	10.810%	$215.9687	$215.97	$215.95	$216.00
Purchase #5	$151.57	13.186%	$171.556	$171.56	$171.55	$171.60
Purchase #6	$177.45	4.476%	$185.3927	$185.39	$185.40	$185.40
Purchase #7	$105.96	6.721%	$113.0816	$113.08	$113.10	$113.10
7 purchase totals =	$1,099.16		$1,188.4861	$1,188.48	$1,188.50	$1,188.50