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	$70.30	9.283%	$76.8259	$76.83	$76.85	$76.80
Purchase #2	$194.40	12.565%	$218.8264	$218.83	$218.85	$218.80
Purchase #3	$166.80	4.626%	$174.5162	$174.52	$174.50	$174.50
Purchase #4	$30.78	10.207%	$33.9217	$33.92	$33.90	$33.90
Purchase #5	$56.26	10.467%	$62.1487	$62.15	$62.15	$62.10
Purchase #6	$28.29	7.440%	$30.3948	$30.39	$30.40	$30.40
Purchase #7	$82.83	7.711%	$89.217	$89.22	$89.20	$89.20
7 purchase totals =	$629.66		$685.8507	$685.86	$685.85	$685.70