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	$89.65	11.808%	$100.2359	$100.24	$100.25	$100.20
Purchase #2	$120.73	12.772%	$136.1496	$136.15	$136.15	$136.10
Purchase #3	$152.82	7.550%	$164.3579	$164.36	$164.35	$164.40
Purchase #4	$178.53	7.669%	$192.2215	$192.22	$192.20	$192.20
Purchase #5	$142.27	9.838%	$156.2665	$156.27	$156.25	$156.30
Purchase #6	$45.51	11.286%	$50.6463	$50.65	$50.65	$50.60
Purchase #7	$98.35	12.362%	$110.508	$110.51	$110.50	$110.50
7 purchase totals =	$827.86		$910.3857	$910.40	$910.35	$910.30