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	$138.53	5.291%	$145.8596	$145.86	$145.85	$145.90
Purchase #2	$179.30	3.692%	$185.9198	$185.92	$185.90	$185.90
Purchase #3	$209.64	4.332%	$218.7216	$218.72	$218.70	$218.70
Purchase #4	$199.93	11.508%	$222.9379	$222.94	$222.95	$222.90
Purchase #5	$23.98	10.157%	$26.4156	$26.42	$26.40	$26.40
Purchase #6	$104.63	9.489%	$114.5583	$114.56	$114.55	$114.60
Purchase #7	$92.39	12.580%	$104.0127	$104.01	$104.00	$104.00
7 purchase totals =	$948.40		$1,018.4255	$1,018.43	$1,018.35	$1,018.40