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	$89.84	10.508%	$99.2804	$99.28	$99.30	$99.30
Purchase #2	$57.97	10.201%	$63.8835	$63.88	$63.90	$63.90
Purchase #3	$76.48	7.294%	$82.0585	$82.06	$82.05	$82.10
Purchase #4	$207.33	3.385%	$214.3481	$214.35	$214.35	$214.30
Purchase #5	$19.73	9.604%	$21.6249	$21.62	$21.60	$21.60
Purchase #6	$96.42	13.298%	$109.2419	$109.24	$109.25	$109.20
Purchase #7	$33.73	11.272%	$37.532	$37.53	$37.55	$37.50
7 purchase totals =	$581.50		$627.9693	$627.96	$628.00	$627.90