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	$51.83	7.861%	$55.9044	$55.90	$55.90	$55.90
Purchase #2	$82.37	9.274%	$90.009	$90.01	$90.00	$90.00
Purchase #3	$17.55	9.280%	$19.1786	$19.18	$19.20	$19.20
Purchase #4	$113.97	6.580%	$121.4692	$121.47	$121.45	$121.50
Purchase #5	$43.65	12.761%	$49.2202	$49.22	$49.20	$49.20
Purchase #6	$81.50	10.239%	$89.8448	$89.84	$89.85	$89.80
Purchase #7	$31.40	13.464%	$35.6277	$35.63	$35.65	$35.60
7 purchase totals =	$422.27		$461.2539	$461.25	$461.25	$461.20