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	$91.44	9.570%	$100.1908	$100.19	$100.20	$100.20
Purchase #2	$13.40	11.227%	$14.9044	$14.90	$14.90	$14.90
Purchase #3	$120.93	8.585%	$131.3118	$131.31	$131.30	$131.30
Purchase #4	$120.52	4.655%	$126.1302	$126.13	$126.15	$126.10
Purchase #5	$211.89	7.182%	$227.1079	$227.11	$227.10	$227.10
Purchase #6	$191.44	11.154%	$212.7932	$212.79	$212.80	$212.80
Purchase #7	$83.50	8.768%	$90.8213	$90.82	$90.80	$90.80
7 purchase totals =	$833.12		$903.2596	$903.25	$903.25	$903.20