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	$86.98	3.324%	$89.8712	$89.87	$89.85	$89.90
Purchase #2	$180.63	6.233%	$191.8887	$191.89	$191.90	$191.90
Purchase #3	$215.75	11.197%	$239.9075	$239.91	$239.90	$239.90
Purchase #4	$85.46	12.404%	$96.0605	$96.06	$96.05	$96.10
Purchase #5	$84.34	6.740%	$90.0245	$90.02	$90.00	$90.00
Purchase #6	$244.70	10.800%	$271.1276	$271.13	$271.15	$271.10
Purchase #7	$113.84	13.107%	$128.761	$128.76	$128.75	$128.80
7 purchase totals =	$1,011.70		$1,107.6410	$1,107.64	$1,107.60	$1,107.70