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	$50.97	7.455%	$54.7698	$54.77	$54.75	$54.80
Purchase #2	$41.55	9.698%	$45.5795	$45.58	$45.60	$45.60
Purchase #3	$58.56	11.830%	$65.4876	$65.49	$65.50	$65.50
Purchase #4	$222.75	11.801%	$249.0367	$249.04	$249.05	$249.00
Purchase #5	$236.61	7.199%	$253.6436	$253.64	$253.65	$253.60
Purchase #6	$89.94	8.477%	$97.5642	$97.56	$97.55	$97.60
Purchase #7	$98.58	5.570%	$104.0709	$104.07	$104.05	$104.10
7 purchase totals =	$798.96		$870.1523	$870.15	$870.15	$870.20