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	$7.89	9.152%	$8.6121	$8.61	$8.60	$8.60
Purchase #2	$86.68	13.217%	$98.1365	$98.14	$98.15	$98.10
Purchase #3	$192.92	6.384%	$205.236	$205.24	$205.25	$205.20
Purchase #4	$137.61	7.194%	$147.5097	$147.51	$147.50	$147.50
Purchase #5	$103.31	5.633%	$109.1295	$109.13	$109.15	$109.10
Purchase #6	$185.34	8.168%	$200.4786	$200.48	$200.50	$200.50
Purchase #7	$70.68	6.572%	$75.3251	$75.33	$75.35	$75.30
7 purchase totals =	$784.43		$844.4275	$844.44	$844.50	$844.30