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	$37.71	12.729%	$42.5101	$42.51	$42.50	$42.50
Purchase #2	$30.41	4.819%	$31.8755	$31.88	$31.90	$31.90
Purchase #3	$144.85	13.389%	$164.244	$164.24	$164.25	$164.20
Purchase #4	$97.46	12.427%	$109.5714	$109.57	$109.55	$109.60
Purchase #5	$228.27	12.862%	$257.6301	$257.63	$257.65	$257.60
Purchase #6	$65.25	4.407%	$68.1256	$68.13	$68.15	$68.10
Purchase #7	$99.46	12.608%	$111.9999	$112.00	$112.00	$112.00
7 purchase totals =	$703.41		$785.9566	$785.96	$786.00	$785.90