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	$30.27	11.683%	$33.8064	$33.81	$33.80	$33.80
Purchase #2	$155.32	8.202%	$168.0593	$168.06	$168.05	$168.10
Purchase #3	$105.93	3.123%	$109.2382	$109.24	$109.25	$109.20
Purchase #4	$78.92	4.373%	$82.3712	$82.37	$82.35	$82.40
Purchase #5	$11.44	8.288%	$12.3881	$12.39	$12.40	$12.40
Purchase #6	$62.74	11.631%	$70.0373	$70.04	$70.05	$70.00
Purchase #7	$80.43	6.839%	$85.9306	$85.93	$85.95	$85.90
7 purchase totals =	$525.05		$561.8311	$561.84	$561.85	$561.80