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	$96.42	9.294%	$105.3813	$105.38	$105.40	$105.40
Purchase #2	$186.59	7.213%	$200.0487	$200.05	$200.05	$200.00
Purchase #3	$53.63	11.311%	$59.6961	$59.70	$59.70	$59.70
Purchase #4	$200.83	11.391%	$223.7065	$223.71	$223.70	$223.70
Purchase #5	$49.65	7.407%	$53.3276	$53.33	$53.35	$53.30
Purchase #6	$91.78	4.730%	$96.1212	$96.12	$96.10	$96.10
Purchase #7	$110.92	9.254%	$121.1845	$121.18	$121.20	$121.20
7 purchase totals =	$789.82		$859.4659	$859.47	$859.50	$859.40