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	$115.55	10.810%	$128.041	$128.04	$128.05	$128.00
Purchase #2	$182.36	4.797%	$191.1078	$191.11	$191.10	$191.10
Purchase #3	$158.82	11.564%	$177.1859	$177.19	$177.20	$177.20
Purchase #4	$104.71	7.772%	$112.8481	$112.85	$112.85	$112.80
Purchase #5	$133.57	7.833%	$144.0325	$144.03	$144.05	$144.00
Purchase #6	$82.61	8.549%	$89.6723	$89.67	$89.65	$89.70
Purchase #7	$125.53	7.849%	$135.3828	$135.38	$135.40	$135.40
7 purchase totals =	$903.15		$978.2704	$978.27	$978.30	$978.20