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	$18.38	10.348%	$20.282	$20.28	$20.30	$20.30
Purchase #2	$198.76	11.822%	$222.2574	$222.26	$222.25	$222.30
Purchase #3	$99.48	6.281%	$105.7283	$105.73	$105.75	$105.70
Purchase #4	$109.47	6.528%	$116.6162	$116.62	$116.60	$116.60
Purchase #5	$63.42	3.175%	$65.4336	$65.43	$65.45	$65.40
Purchase #6	$150.87	11.573%	$168.3302	$168.33	$168.35	$168.30
Purchase #7	$219.56	8.526%	$238.2797	$238.28	$238.30	$238.30
7 purchase totals =	$859.94		$936.9274	$936.93	$937.00	$936.90