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	$149.90	8.675%	$162.9038	$162.90	$162.90	$162.90
Purchase #2	$49.93	7.606%	$53.7277	$53.73	$53.75	$53.70
Purchase #3	$131.97	13.744%	$150.108	$150.11	$150.10	$150.10
Purchase #4	$165.69	5.268%	$174.4185	$174.42	$174.40	$174.40
Purchase #5	$142.58	12.230%	$160.0175	$160.02	$160.00	$160.00
Purchase #6	$99.44	9.539%	$108.9256	$108.93	$108.95	$108.90
Purchase #7	$81.55	11.440%	$90.8793	$90.88	$90.90	$90.90
7 purchase totals =	$821.06		$900.9804	$900.99	$901.00	$900.90