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	$39.43	6.378%	$41.9448	$41.94	$41.95	$41.90
Purchase #2	$35.89	7.309%	$38.5132	$38.51	$38.50	$38.50
Purchase #3	$140.80	7.658%	$151.5825	$151.58	$151.60	$151.60
Purchase #4	$125.97	9.568%	$138.0228	$138.02	$138.00	$138.00
Purchase #5	$168.33	11.789%	$188.1744	$188.17	$188.15	$188.20
Purchase #6	$44.54	9.765%	$48.8893	$48.89	$48.90	$48.90
Purchase #7	$167.52	11.644%	$187.026	$187.03	$187.05	$187.00
7 purchase totals =	$722.48		$794.1530	$794.14	$794.15	$794.10