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	$197.94	12.809%	$223.2941	$223.29	$223.30	$223.30
Purchase #2	$153.75	9.848%	$168.8913	$168.89	$168.90	$168.90
Purchase #3	$167.37	13.865%	$190.5759	$190.58	$190.60	$190.60
Purchase #4	$108.75	6.263%	$115.561	$115.56	$115.55	$115.60
Purchase #5	$199.37	4.772%	$208.8839	$208.88	$208.90	$208.90
Purchase #6	$44.44	6.494%	$47.3259	$47.33	$47.35	$47.30
Purchase #7	$30.90	5.143%	$32.4892	$32.49	$32.50	$32.50
7 purchase totals =	$902.52		$987.0213	$987.02	$987.10	$987.10