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	$47.90	9.232%	$52.3221	$52.32	$52.30	$52.30
Purchase #2	$14.59	6.337%	$15.5146	$15.51	$15.50	$15.50
Purchase #3	$101.41	7.535%	$109.0512	$109.05	$109.05	$109.10
Purchase #4	$60.62	3.698%	$62.8617	$62.86	$62.85	$62.90
Purchase #5	$76.65	7.279%	$82.2294	$82.23	$82.25	$82.20
Purchase #6	$249.29	12.123%	$279.5114	$279.51	$279.50	$279.50
Purchase #7	$165.95	13.437%	$188.2487	$188.25	$188.25	$188.20
7 purchase totals =	$716.41		$789.7391	$789.73	$789.70	$789.70