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	$128.33	8.801%	$139.6243	$139.62	$139.60	$139.60
Purchase #2	$85.81	10.234%	$94.5918	$94.59	$94.60	$94.60
Purchase #3	$140.66	4.173%	$146.5297	$146.53	$146.55	$146.50
Purchase #4	$81.93	9.626%	$89.8166	$89.82	$89.80	$89.80
Purchase #5	$51.88	11.103%	$57.6402	$57.64	$57.65	$57.60
Purchase #6	$45.85	9.853%	$50.3676	$50.37	$50.35	$50.40
Purchase #7	$60.78	13.112%	$68.7495	$68.75	$68.75	$68.70
7 purchase totals =	$595.24		$647.3197	$647.32	$647.30	$647.20