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	$6.62	7.285%	$7.1023	$7.10	$7.10	$7.10
Purchase #2	$122.61	5.177%	$128.9575	$128.96	$128.95	$129.00
Purchase #3	$81.92	9.367%	$89.5934	$89.59	$89.60	$89.60
Purchase #4	$212.41	6.330%	$225.8556	$225.86	$225.85	$225.90
Purchase #5	$174.53	8.472%	$189.3162	$189.32	$189.30	$189.30
Purchase #6	$225.47	12.472%	$253.5906	$253.59	$253.60	$253.60
Purchase #7	$54.49	3.765%	$56.5415	$56.54	$56.55	$56.50
7 purchase totals =	$878.05		$950.9571	$950.96	$950.95	$951.00