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	$128.31	13.681%	$145.8641	$145.86	$145.85	$145.90
Purchase #2	$222.79	7.300%	$239.0537	$239.05	$239.05	$239.10
Purchase #3	$198.84	6.793%	$212.3472	$212.35	$212.35	$212.30
Purchase #4	$116.64	3.643%	$120.8892	$120.89	$120.90	$120.90
Purchase #5	$86.89	4.525%	$90.8218	$90.82	$90.80	$90.80
Purchase #6	$99.73	7.211%	$106.9215	$106.92	$106.90	$106.90
Purchase #7	$78.83	3.414%	$81.5213	$81.52	$81.50	$81.50
7 purchase totals =	$932.03		$997.4188	$997.41	$997.35	$997.40