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	$104.63	4.391%	$109.2243	$109.22	$109.20	$109.20
Purchase #2	$228.30	8.465%	$247.6256	$247.63	$247.65	$247.60
Purchase #3	$47.91	8.464%	$51.9651	$51.97	$51.95	$52.00
Purchase #4	$221.83	11.814%	$248.037	$248.04	$248.05	$248.00
Purchase #5	$83.68	7.301%	$89.7895	$89.79	$89.80	$89.80
Purchase #6	$212.86	4.683%	$222.8282	$222.83	$222.85	$222.80
Purchase #7	$28.49	9.868%	$31.3014	$31.30	$31.30	$31.30
7 purchase totals =	$927.70		$1,000.7711	$1,000.78	$1,000.80	$1,000.70