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	$30.60	3.569%	$31.6921	$31.69	$31.70	$31.70
Purchase #2	$131.57	12.831%	$148.4517	$148.45	$148.45	$148.50
Purchase #3	$8.88	8.197%	$9.6079	$9.61	$9.60	$9.60
Purchase #4	$151.28	6.119%	$160.5368	$160.54	$160.55	$160.50
Purchase #5	$59.32	3.719%	$61.5261	$61.53	$61.55	$61.50
Purchase #6	$98.50	13.157%	$111.4596	$111.46	$111.45	$111.50
Purchase #7	$245.47	9.208%	$268.0729	$268.07	$268.05	$268.10
7 purchase totals =	$725.62		$791.3471	$791.35	$791.35	$791.40