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	$32.38	6.809%	$34.5848	$34.58	$34.60	$34.60
Purchase #2	$94.77	3.543%	$98.1277	$98.13	$98.15	$98.10
Purchase #3	$89.33	6.490%	$95.1275	$95.13	$95.15	$95.10
Purchase #4	$173.25	6.758%	$184.9582	$184.96	$184.95	$185.00
Purchase #5	$142.28	8.196%	$153.9413	$153.94	$153.95	$153.90
Purchase #6	$159.84	5.464%	$168.5737	$168.57	$168.55	$168.60
Purchase #7	$152.37	10.196%	$167.9056	$167.91	$167.90	$167.90
7 purchase totals =	$844.22		$903.2188	$903.22	$903.25	$903.20