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	$69.66	4.482%	$72.7822	$72.78	$72.80	$72.80
Purchase #2	$128.88	12.407%	$144.8701	$144.87	$144.85	$144.90
Purchase #3	$88.87	4.228%	$92.6274	$92.63	$92.65	$92.60
Purchase #4	$84.35	8.818%	$91.788	$91.79	$91.80	$91.80
Purchase #5	$203.78	10.760%	$225.7067	$225.71	$225.70	$225.70
Purchase #6	$48.81	12.422%	$54.8732	$54.87	$54.85	$54.90
Purchase #7	$101.69	8.213%	$110.0418	$110.04	$110.05	$110.00
7 purchase totals =	$726.04		$792.6894	$792.69	$792.70	$792.70