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	$104.70	6.799%	$111.8186	$111.82	$111.80	$111.80
Purchase #2	$168.87	5.805%	$178.6729	$178.67	$178.65	$178.70
Purchase #3	$84.70	8.583%	$91.9698	$91.97	$91.95	$92.00
Purchase #4	$224.30	9.567%	$245.7588	$245.76	$245.75	$245.80
Purchase #5	$84.29	13.214%	$95.4281	$95.43	$95.45	$95.40
Purchase #6	$35.63	6.374%	$37.9011	$37.90	$37.90	$37.90
Purchase #7	$80.64	11.266%	$89.7249	$89.72	$89.70	$89.70
7 purchase totals =	$783.13		$851.2742	$851.27	$851.20	$851.30