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	$67.93	6.742%	$72.5098	$72.51	$72.50	$72.50
Purchase #2	$194.88	5.666%	$205.9219	$205.92	$205.90	$205.90
Purchase #3	$62.56	9.120%	$68.2655	$68.27	$68.25	$68.30
Purchase #4	$169.96	6.460%	$180.9394	$180.94	$180.95	$180.90
Purchase #5	$114.82	10.720%	$127.1287	$127.13	$127.15	$127.10
Purchase #6	$87.38	13.638%	$99.2969	$99.30	$99.30	$99.30
Purchase #7	$171.27	10.486%	$189.2294	$189.23	$189.25	$189.20
7 purchase totals =	$868.80		$943.2916	$943.30	$943.30	$943.20