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	$136.26	9.162%	$148.7441	$148.74	$148.75	$148.70
Purchase #2	$215.74	3.266%	$222.7861	$222.79	$222.80	$222.80
Purchase #3	$155.75	5.858%	$164.8738	$164.87	$164.85	$164.90
Purchase #4	$220.83	11.174%	$245.5055	$245.51	$245.50	$245.50
Purchase #5	$115.30	10.851%	$127.8112	$127.81	$127.80	$127.80
Purchase #6	$45.87	3.287%	$47.3777	$47.38	$47.40	$47.40
Purchase #7	$41.81	3.755%	$43.38	$43.38	$43.40	$43.40
7 purchase totals =	$931.56		$1,000.4784	$1,000.48	$1,000.50	$1,000.50