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	$21.31	12.844%	$24.0471	$24.05	$24.05	$24.00
Purchase #2	$193.67	13.270%	$219.37	$219.37	$219.35	$219.40
Purchase #3	$42.76	6.621%	$45.5911	$45.59	$45.60	$45.60
Purchase #4	$6.48	8.269%	$7.0158	$7.02	$7.00	$7.00
Purchase #5	$40.91	4.232%	$42.6413	$42.64	$42.65	$42.60
Purchase #6	$18.53	9.283%	$20.2501	$20.25	$20.25	$20.30
Purchase #7	$202.84	4.464%	$211.8948	$211.89	$211.90	$211.90
7 purchase totals =	$526.50		$570.8102	$570.81	$570.80	$570.80