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	$111.62	10.227%	$123.0354	$123.04	$123.05	$123.00
Purchase #2	$129.44	10.343%	$142.828	$142.83	$142.85	$142.80
Purchase #3	$155.29	8.864%	$169.0549	$169.05	$169.05	$169.10
Purchase #4	$155.88	3.863%	$161.9016	$161.90	$161.90	$161.90
Purchase #5	$91.32	4.864%	$95.7618	$95.76	$95.75	$95.80
Purchase #6	$191.27	9.554%	$209.5439	$209.54	$209.55	$209.50
Purchase #7	$165.51	12.771%	$186.6473	$186.65	$186.65	$186.60
7 purchase totals =	$1,000.33		$1,088.7729	$1,088.77	$1,088.80	$1,088.70