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	$246.82	11.154%	$274.3503	$274.35	$274.35	$274.40
Purchase #2	$197.39	6.704%	$210.623	$210.62	$210.60	$210.60
Purchase #3	$95.80	3.282%	$98.9442	$98.94	$98.95	$98.90
Purchase #4	$13.62	13.870%	$15.5091	$15.51	$15.50	$15.50
Purchase #5	$128.43	6.801%	$137.1645	$137.16	$137.15	$137.20
Purchase #6	$82.48	10.147%	$90.8492	$90.85	$90.85	$90.80
Purchase #7	$89.64	11.284%	$99.755	$99.76	$99.75	$99.80
7 purchase totals =	$854.18		$927.1953	$927.19	$927.15	$927.20