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	$116.66	10.581%	$129.0038	$129.00	$129.00	$129.00
Purchase #2	$177.99	11.415%	$198.3076	$198.31	$198.30	$198.30
Purchase #3	$191.98	12.408%	$215.8009	$215.80	$215.80	$215.80
Purchase #4	$30.67	9.551%	$33.5993	$33.60	$33.60	$33.60
Purchase #5	$59.30	10.601%	$65.5864	$65.59	$65.60	$65.60
Purchase #6	$95.41	3.345%	$98.6015	$98.60	$98.60	$98.60
Purchase #7	$89.30	11.783%	$99.8222	$99.82	$99.80	$99.80
7 purchase totals =	$761.31		$840.7217	$840.72	$840.70	$840.70