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	$21.51	7.115%	$23.0404	$23.04	$23.05	$23.00
Purchase #2	$210.37	11.465%	$234.4889	$234.49	$234.50	$234.50
Purchase #3	$85.91	4.786%	$90.0217	$90.02	$90.00	$90.00
Purchase #4	$99.66	9.779%	$109.4058	$109.41	$109.40	$109.40
Purchase #5	$231.45	5.546%	$244.2862	$244.29	$244.30	$244.30
Purchase #6	$78.37	9.729%	$85.9946	$85.99	$86.00	$86.00
Purchase #7	$59.38	3.416%	$61.4084	$61.41	$61.40	$61.40
7 purchase totals =	$786.65		$848.6460	$848.65	$848.65	$848.60