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	$89.87	7.798%	$96.8781	$96.88	$96.90	$96.90
Purchase #2	$91.65	3.478%	$94.8376	$94.84	$94.85	$94.80
Purchase #3	$110.90	8.775%	$120.6315	$120.63	$120.65	$120.60
Purchase #4	$128.95	10.626%	$142.6522	$142.65	$142.65	$142.70
Purchase #5	$130.28	6.831%	$139.1794	$139.18	$139.20	$139.20
Purchase #6	$42.90	13.306%	$48.6083	$48.61	$48.60	$48.60
Purchase #7	$85.46	4.503%	$89.3083	$89.31	$89.30	$89.30
7 purchase totals =	$680.01		$732.0954	$732.10	$732.15	$732.10