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	$59.44	12.440%	$66.8343	$66.83	$66.85	$66.80
Purchase #2	$169.55	11.118%	$188.4006	$188.40	$188.40	$188.40
Purchase #3	$88.40	3.460%	$91.4586	$91.46	$91.45	$91.50
Purchase #4	$25.37	9.609%	$27.8078	$27.81	$27.80	$27.80
Purchase #5	$179.92	13.613%	$204.4125	$204.41	$204.40	$204.40
Purchase #6	$155.87	3.221%	$160.8906	$160.89	$160.90	$160.90
Purchase #7	$49.28	11.728%	$55.0596	$55.06	$55.05	$55.10
7 purchase totals =	$727.83		$794.8640	$794.86	$794.85	$794.90