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	$94.72	11.820%	$105.9159	$105.92	$105.90	$105.90
Purchase #2	$108.39	11.594%	$120.9567	$120.96	$120.95	$121.00
Purchase #3	$63.27	13.633%	$71.8956	$71.90	$71.90	$71.90
Purchase #4	$45.76	13.113%	$51.7605	$51.76	$51.75	$51.80
Purchase #5	$226.52	10.160%	$249.5344	$249.53	$249.55	$249.50
Purchase #6	$191.66	4.630%	$200.5339	$200.53	$200.55	$200.50
Purchase #7	$69.29	10.825%	$76.7906	$76.79	$76.80	$76.80
7 purchase totals =	$799.61		$877.3876	$877.39	$877.40	$877.40