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	$162.42	7.830%	$175.1375	$175.14	$175.15	$175.10
Purchase #2	$80.43	12.639%	$90.5955	$90.60	$90.60	$90.60
Purchase #3	$175.57	7.399%	$188.5604	$188.56	$188.55	$188.60
Purchase #4	$145.30	13.518%	$164.9417	$164.94	$164.95	$164.90
Purchase #5	$24.65	9.587%	$27.0132	$27.01	$27.00	$27.00
Purchase #6	$182.52	7.445%	$196.1086	$196.11	$196.10	$196.10
Purchase #7	$59.81	11.536%	$66.7097	$66.71	$66.70	$66.70
7 purchase totals =	$830.70		$909.0666	$909.07	$909.05	$909.00