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	$187.55	11.652%	$209.4033	$209.40	$209.40	$209.40
Purchase #2	$73.39	12.474%	$82.5447	$82.54	$82.55	$82.50
Purchase #3	$183.29	8.760%	$199.3462	$199.35	$199.35	$199.30
Purchase #4	$80.74	10.699%	$89.3784	$89.38	$89.40	$89.40
Purchase #5	$18.25	13.738%	$20.7572	$20.76	$20.75	$20.80
Purchase #6	$160.66	3.239%	$165.8638	$165.86	$165.85	$165.90
Purchase #7	$79.79	3.303%	$82.4255	$82.43	$82.45	$82.40
7 purchase totals =	$783.67		$849.7191	$849.72	$849.75	$849.70