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	$46.90	6.697%	$50.0409	$50.04	$50.05	$50.00
Purchase #2	$100.71	13.507%	$114.3129	$114.31	$114.30	$114.30
Purchase #3	$133.66	7.249%	$143.349	$143.35	$143.35	$143.30
Purchase #4	$229.81	10.450%	$253.8251	$253.83	$253.85	$253.80
Purchase #5	$220.87	7.370%	$237.1481	$237.15	$237.15	$237.10
Purchase #6	$92.40	7.418%	$99.2542	$99.25	$99.25	$99.30
Purchase #7	$19.53	5.250%	$20.5553	$20.56	$20.55	$20.60
7 purchase totals =	$843.88		$918.4855	$918.49	$918.50	$918.40