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	$12.32	9.320%	$13.4682	$13.47	$13.45	$13.50
Purchase #2	$97.53	12.647%	$109.8646	$109.86	$109.85	$109.90
Purchase #3	$27.86	13.199%	$31.5372	$31.54	$31.55	$31.50
Purchase #4	$109.93	13.501%	$124.7716	$124.77	$124.75	$124.80
Purchase #5	$207.40	6.588%	$221.0635	$221.06	$221.05	$221.10
Purchase #6	$56.92	8.794%	$61.9255	$61.93	$61.95	$61.90
Purchase #7	$104.51	4.144%	$108.8409	$108.84	$108.85	$108.80
7 purchase totals =	$616.47		$671.4715	$671.47	$671.45	$671.50