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	$228.50	5.869%	$241.9107	$241.91	$241.90	$241.90
Purchase #2	$44.84	12.482%	$50.4369	$50.44	$50.45	$50.40
Purchase #3	$127.73	9.107%	$139.3624	$139.36	$139.35	$139.40
Purchase #4	$42.84	9.291%	$46.8203	$46.82	$46.80	$46.80
Purchase #5	$90.78	12.212%	$101.8661	$101.87	$101.85	$101.90
Purchase #6	$25.72	9.332%	$28.1202	$28.12	$28.10	$28.10
Purchase #7	$19.25	8.375%	$20.8622	$20.86	$20.85	$20.90
7 purchase totals =	$579.66		$629.3788	$629.38	$629.30	$629.40