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	$17.96	12.708%	$20.2424	$20.24	$20.25	$20.20
Purchase #2	$179.49	9.260%	$196.1108	$196.11	$196.10	$196.10
Purchase #3	$57.73	10.274%	$63.6612	$63.66	$63.65	$63.70
Purchase #4	$205.85	7.560%	$221.4123	$221.41	$221.40	$221.40
Purchase #5	$233.69	6.565%	$249.0317	$249.03	$249.05	$249.00
Purchase #6	$86.61	4.458%	$90.4711	$90.47	$90.45	$90.50
Purchase #7	$99.55	10.639%	$110.1411	$110.14	$110.15	$110.10
7 purchase totals =	$880.88		$951.0706	$951.06	$951.05	$951.00