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	$11.86	3.498%	$12.2749	$12.27	$12.25	$12.30
Purchase #2	$19.58	8.275%	$21.2002	$21.20	$21.20	$21.20
Purchase #3	$96.33	5.592%	$101.7168	$101.72	$101.70	$101.70
Purchase #4	$98.83	10.624%	$109.3297	$109.33	$109.35	$109.30
Purchase #5	$65.55	12.322%	$73.6271	$73.63	$73.65	$73.60
Purchase #6	$164.98	8.697%	$179.3283	$179.33	$179.35	$179.30
Purchase #7	$89.96	7.281%	$96.51	$96.51	$96.50	$96.50
7 purchase totals =	$547.09		$593.9870	$593.99	$594.00	$593.90