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	$76.29	4.714%	$79.8863	$79.89	$79.90	$79.90
Purchase #2	$20.63	9.471%	$22.5839	$22.58	$22.60	$22.60
Purchase #3	$148.77	10.634%	$164.5902	$164.59	$164.60	$164.60
Purchase #4	$121.58	4.749%	$127.3538	$127.35	$127.35	$127.40
Purchase #5	$137.41	7.337%	$147.4918	$147.49	$147.50	$147.50
Purchase #6	$185.26	12.871%	$209.1048	$209.10	$209.10	$209.10
Purchase #7	$135.79	4.702%	$142.1748	$142.17	$142.15	$142.20
7 purchase totals =	$825.73		$893.1856	$893.17	$893.20	$893.30