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	$83.90	7.555%	$90.2386	$90.24	$90.25	$90.20
Purchase #2	$93.65	5.543%	$98.841	$98.84	$98.85	$98.80
Purchase #3	$89.37	11.870%	$99.9782	$99.98	$100.00	$100.00
Purchase #4	$52.42	10.530%	$57.9398	$57.94	$57.95	$57.90
Purchase #5	$64.63	12.717%	$72.849	$72.85	$72.85	$72.80
Purchase #6	$8.29	12.764%	$9.3481	$9.35	$9.35	$9.30
Purchase #7	$158.28	9.656%	$173.5635	$173.56	$173.55	$173.60
7 purchase totals =	$550.54		$602.7582	$602.76	$602.80	$602.60