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	$35.48	11.654%	$39.6148	$39.61	$39.60	$39.60
Purchase #2	$244.57	13.258%	$276.9951	$277.00	$277.00	$277.00
Purchase #3	$152.95	9.308%	$167.1866	$167.19	$167.20	$167.20
Purchase #4	$53.86	11.244%	$59.916	$59.92	$59.90	$59.90
Purchase #5	$91.80	9.535%	$100.5531	$100.55	$100.55	$100.60
Purchase #6	$74.96	4.435%	$78.2845	$78.28	$78.30	$78.30
Purchase #7	$249.94	8.663%	$271.5923	$271.59	$271.60	$271.60
7 purchase totals =	$903.56		$994.1424	$994.14	$994.15	$994.20