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	$98.86	12.688%	$111.4034	$111.40	$111.40	$111.40
Purchase #2	$79.72	12.751%	$89.8851	$89.89	$89.90	$89.90
Purchase #3	$80.62	9.480%	$88.2628	$88.26	$88.25	$88.30
Purchase #4	$85.25	11.135%	$94.7426	$94.74	$94.75	$94.70
Purchase #5	$91.97	4.224%	$95.8548	$95.85	$95.85	$95.90
Purchase #6	$161.80	4.624%	$169.2816	$169.28	$169.30	$169.30
Purchase #7	$124.84	11.521%	$139.2228	$139.22	$139.20	$139.20
7 purchase totals =	$723.06		$788.6531	$788.64	$788.65	$788.70