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	$250.52	6.744%	$267.4151	$267.42	$267.40	$267.40
Purchase #2	$81.48	10.434%	$89.9816	$89.98	$90.00	$90.00
Purchase #3	$216.69	8.567%	$235.2538	$235.25	$235.25	$235.30
Purchase #4	$74.28	11.411%	$82.7561	$82.76	$82.75	$82.80
Purchase #5	$39.64	5.232%	$41.714	$41.71	$41.70	$41.70
Purchase #6	$80.87	6.816%	$86.3821	$86.38	$86.40	$86.40
Purchase #7	$106.35	7.695%	$114.5336	$114.53	$114.55	$114.50
7 purchase totals =	$849.83		$918.0363	$918.03	$918.05	$918.10